I strongly doubt it has a legal copy of Windows 7. And this desktop is so old, the only valid Windows that can be installed on it is XP. The GX620 dates back to Windows 2000 days. Dell has no Vista drivers for this model. I am not in the least surprised that Vista will not activate on this PC. If I were you, I'd return the PC.  If you don't want to return the PC, you'll need to either buy a real copy of Windows 7, or install Linux on it.  
Hi, Im not the best when it comes to the ins & outs of computers and this looks like the kind of place I could get some sound advice so here goes..... I purchased this machine off ebay and it came with windows 7 64 bit pre-installed and with recovery disc. I have tried to activate this using belarc software to obtain the license key. No such luck. Im getting error code  0Xc004e003. I also have no option to activate via telephone, only by typing a different key. I thought I would give my copy of Vista 32 bit that came with my dell laptop a go so made a partition in hard drive, installed Vista but am getting the same error code when trying to activate. I was thinking the copy of Win7 already installed may be a bit dodgy but my copy of Vista is 100% genuine. I have read some posts on here similar to this that advise to purchase a OEM copy of win7 which I understand but I have the OEM Vista copy....and its not working. Am I missing a trick here? Any help would be welcome. Thanks in advance.     
Help! dell gx620 ssf vista OS not activating