sometimes display drivers are too up-to-date and they surpass the given gfx card edition and don't communicate so well retroactively.. also, never a good idea to leave browsers open, but that is just an opinion. if you go into your BIOS, there are some options that you might find that concern your display config. don't change anything unless you are confident you will not hose up the settings, just report back what you saw that could pertain to your display. I want you to also try to get information from a handy app we affectionately call S I W. it is free to download a watered down version, it basically tells you exactly what you have in your PC, including BIOS and GPU temperatures. it can get puzzling because the information SIW provides is seamingly endless, but we need the information that is specific to this PC adversity you are facing. you can also do a screen grab and post up the image of information pertaining to this issue. watch out though, BC puts tight limits on your attachment upload file size tiotals. and you may have to clean them out using your BC profile manager before you can put up another image attachment.
This one time i saw something peculiar. the poor guys computer was powering up and then went blank.boom/bam - no video signal. he left a foxtrotting disk in his optical drive and BIOS was prioritizing boot from it. we had to go into his BIOS to get the boot priority set right and then he was set. it made me wonder though, that disk being in there on startup, did BIOS change automatically to prioritize it? i didn't think that would happen, then i thought of my gfx incursions, when i had to get by on onboard, when i did install a gfx card i didn;t have to go into BIOS and change anything, and this happened 3 times going back and forth between onboard and gfx card installs
I read somewhere about how gfx card memory plays see-saw with ram addresses, but that might not pertain to 64-bit.. is your gfx memory gddr3 or gddr5? gddr5 pulls more power. there is yet another handy app called memtest86+ that takes until christmas to diagnose your system ram, so it might be something you start running at bedtime and see the next day what it came up with.
I used to also suffer from power outages. I finally parted with a few bucks and bought a cheapie UPS after so many power outages finally blew the bulbs in my monitor. it was worth it.
Also, you have other options to try. you can try to use your onboard video VGA output to see if that is ok to run everything, or you can play swap -out with other PCs. just clean all current drivers out before installing and reinstalling back and forth. Speaking of VGA.....is your monitor using VGA input out of your 660 or DVI?
The next thing is power supply. what is your make/model/wattage/rail amps etc? I don't think SIW can tell you anything about that, but other apps might.
Apologies for going off on tangents.