I recently uninstall-ed windows 32 bit (OEM) and re-installed windows 64 bit (OEM). Everything is working well, but the system will just blue screen or lock up without blue screen.
The only hardware difference, is that I had 8 gigs of gskill ram plugged in previously, so now windows is of course recognizing the 2nd set of 4 gigs.
So far it has occurred 3 times when playing battlefield bad company 2 (2 blue screens 1 pure lock up).
Since those lock ups, I have made 1 hardware change, from a gtx 260, to an asus gtx 560ti and have not had any problems with bad company 2, but I haven't played for very long.
However it has now locked up twice when I tried to install drivers for my phone, when I plug my phone into my computer via USB it asks to install drivers, but when I click ok, it partially locks up, then goes into a full lock up, but no BSOD.
32 bit windows never locked up in the year I used it, no hardware changes until the 64 bit recognized additional ram, and I swapped out the graphics card.
I am assuming you did a clean install of Windows 7 64 bit, since you cannot not directly from 1 32 bit version of an OS to a 64 bit version. Did you install 64 bit versions of all your drivers, since a 64 bit OS can not use 32 Bit drivers.