This page should help with the BIST (Built In Self Test). Especially this sentence from that page: All that you have posted would certainly appear to be a possible PSU problem.
This is second time I've left this 8930 off for about a week.  Last time, the hardware reset procedure to drain the power worked to bring it back alive.  Prior to that long outage, it worked fine.  Since then, it had worked fine, and even does auto system update so a reboot worked fine.  This time that hardware reset procedure with the power button pressed with and without power cord plugges in does not work.  I'm getting the amber code 2,1 on the power button.  Have removed all externals, have replaced CMOS battery, have left battery out for more than 30 seconds, have pressed power button with battery out to reset CMOS... no joy... still getting that same amber code 2,1... I thought it might be the CMOS battery drained out... this machine is 4 years old... one year out of the 3 yr NBD that I bought with it...  The Power Supply test button works most of the time, but sometimes after plugging in the power cord, no response... could it be a flaky PSU?  When the button does bring up the green light, I noticed that the GPU and CPU fans kick on but the one inside the PSU does not move.  According to the BIST, that is a PSU failure, but reading the related threads, that didn't seem to be a clear verdict. Should I look at replacing the PSU first?  I see secondary market boards are around $100-$200, and the renewed motherboard or from DELL is around $699.  I'd hate to have to replace the board so looking for help in diagnosing with all other steps before that.  Thanks for any help you can provide.  
XPS 8930, off a week, no power, code 2-1 says motherboard failure?