I feel compel to write this to help those who will encounter the problem I face -lrb- and mention here -rrb- . I be one of the many people who want to avoid rent a modem from Comcast and buy this modem base on the stellar review , only to find that on the day of installation\/activation that it `` do not work '' . do not work mean experience the same symptom that be be mention here several time - `` modem connect but then resets\/power cycles\/disconnects itself within a few minute . '' this happen to I on the day i activate my Comcast internet . the technician spend 1.5 hour try to figure it out and end up loan I a Comcast modem -lrb- Motorola SB5120 docsis2 -rrb- , which come up almost instantly and activate just as fast -lrb- go figure -rrb- . he suggest I return this modem as it be defective , in he opinion . I do not like this since the probability of this be very small . but I see what I see and could not get past the first page of Comcast self activation screen with this modem . before the web page for self activation could proceed , after typing my account info and phone number , the modem would conveniently lose connection . at one point I do get to the next screen where it be scanning for device , but the modem cut out thereby hang the process . the modem be pack up in the box for return to Amazon when I could not shake how much this bother I and by my bad luck . so I come back here and read pretty much every review . what I find be there be several people who experience the EXACT same symptom while try several of the same modem . there be two review that stand out . one be from a person who mention the Comcast technician moan when he see it be this modem , indicate that the technician be aware of difficulty use this modem . the person mention that after 70 minute of try to get the modem to connect the technician advise he to leave the modem power on and hook up for awhile and to try activate later . the person do this and be successful in activate the modem . the other review be from a person who be admirably persistent . he review talk of several attempt to connect and refusal to accept that the modem be defective . he end up leave the modem power on and connected overnight so the modem could `` download firmware '' . the next day he be able to activate after two attempt with Comcast self activation process . lastly , I notice for I that if I leave the modem power on and connected but make no attempt to activate it via Comcast web site , the modem retain connection -lrb- via indicator light -rrb- for prolonged period of time . it only seem to lose connection when I try to activate . base on this I feel something be break with Comcast activation process specifically for this modem or perhaps Comcast be intentionally make it difficult to activate this modem to convince customer to rent a `` reliable '' modem from they . to be honest , it almost work for I . after sit there watch the technician agonize try to get the modem to work , I be tempt to rent the modem and move on with life . so as one last hail Mary attempt , this be what I do : 1 . take the modem back out of the box and leave the Motorola sb6121 power on and connect to cable outlet overnight just to entertain the possibility that some firmware or info need to be download to the modem and that for some reason it take a long time to do so . 2 . the next morning I try Comcast 's self activation process . 3 . every time win7 's network icon in the lower right corner of my screen indicate that a internet connection be establish -lrb- vs. exclamation mark -rrb- I immediately open a ie window and start the activation process with my account and phone # . the modem still lose connection when I do this but I keep on try . 4 . it take I about 4 try to succeed . each time I try , I start back on the account and phone # page . but each time it get further and further in the activation process . attempt # 1 : account\/phone # screen - -rrb- retrieve Device Information - -rrb- Modem lose connection . attempt # 2 : account\/phone # screen - -rrb- retrieve Device Information - -rrb- list of device detect -lrb- screen show my motr sb6121 modem and a dtv box both show as `` inactive '' - -rrb- Modem lose connection . -lrb- a thing to note here be that Comcast 's activation system could specifically identify this modem . this mean it be in they system and they system be able to communicate with it -rrb- Attempt # 3 : account\/phone # screen - -rrb- retrieve Device Information - -rrb- list device detect - -rrb- click `` Rescan '' device -lrb- modem -rrb- - -rrb- hit `` next '' to activate then get to screen where it say `` activate device - this may take 10 minute '' - -rrb- Modem lose connection Attempt # 4 : this be not a real attempt because all I do be leave the web browser in the previous `` activate device '' screen and wait for the modem to re-establish connection again . I step away for a few minute and when I come back I get a screen that state `` Device Activate '' -lrb- and some other instruction that do not matter -rrb- hallelujah ! also note , no phone call have to be make to Comcast to activate this modem . at this point , this modem which be lose connection all the time before , now have a seemingly rock solid connection !!! I be use the connection now with this modem as I type this . I have do some basic testing , stream video , surf the net , etc. . no loss of connection ! I do a speed test and I be get 25mbp down and 3.8 mbp up . base on my experience so far , it be in my opinion that this modem work and be as good as what the majority of the reviewer here have state . the problem lie in Comcast 's self activation process which be suspicious . what do not make sense to I be the fact that modem can hold a solid connection if you do not attempt to activate and after it be successfully activate . it be only when I try to go through the self activate process that I see problem . I can not say much about whether step # 1 help but it can not hurt to try . I mention it only to inform people of what exactly I do . I truly hope this help people . Amazon be top notch . this modem be now do what it be suppose to do with no issue . I 'll come back and update this review in about a month to report if it still hold true . I think it will but we 'll see . and lastly , thanks for the people who share they experience here . if it be not for they I would have return the modem back to Amazon and go through the hassle of find another modem or give in and rent one from Comcast . I be try to pay it forward with this review .