The problem is: my PC never ever hangs, and it NEVER reboots under light or heavy normal 3D games, from UT99 to FIFA07 and even UT2004 with 1024x768 resolution (32bit color) and everything tunned to max quality, and it doesn't even stutters with this GT.
It only reboots: in certain websites (using FireFox), like hi5, gamespot, devianart, photobucket most times and filefront some times, but it never reboots in wings forums, beyondunreal or other normal forums, and some isolated events in another program (that now with the chipset update I apllied now seems to run fine).
And I have already cleaned cache, and it auto deletes any cookies at app closing.
Still, no BSODs, no error or warning events in the log (be it either in applications, security and even system), so I don't really what is happening.
Also I can't open the case since it's still in warranty until the end of this month, so I can't really evaluate anything from it, mostly if there are bad caps or not (but still, even with bad caps, the software and moments are too exact to be the mobo).
And what I mean about BIOS messed after sudden shutdown or normal shutdown from power when the PC is already off, is that sometimes it looses all the settings (including time), other times it just modifies some settings by itself, making me loading the default settings and then adjust the boot order and CPU settings again.
So it's hardly the PSU (since this one is a new one) and since the PC strangelly never complains when running some heavier programs and games, even if for hours.
RAM is ok, CPU is ok i guess, the GCard is new and it didn't even passed from 70ºC in UT2004 in a 28ºC environment (even cooler than my old active cooling one, since this is passive/silent).
HDs are fine, since no error was ever given and I already made a 12Gb transfer from a disk to the other, during 40 min or more, and it didn't even made any noise.
All temperatures are fine, also all the clocks (except the CPU one, which is a bit overclocked [+2/7MHz] and which is like that since I bought my PC 2 years ago).
But still yesterday I searched further about this issue, and I found that an outdated bios can give some issues. My bios version is 0901 and the most recent and stable one is the 0904 (there's even a more recent one, but it's still in beta), and the updating of the bios solved some weird reboot problems to some people. And now that I think about that, I never had reboot problems with the GS, which had a 64bit memory interface and Turbo Cache, but these reboots started to happen just exactly like they are happening now with an ATIRadeon which hadn't TC and had a 128bit memory interface.
This new GT one also have no TC and has a 128bit interface, so I am guessing that either the motherboard as a whole has a really serious issue with this kind of GCards, or simply the BIOS/CMOS is outdated and needs to be flashed.
Of course, I won't update myself, since I don't trust the power here (since my mom sometimes forgets there are PCs on and by turning an extra machine when there is already another running... you know what I am talkign about LOL), and also since it seems that I need to burn a disk and I don't have any driver for it. So I will have to get my PC to the store AGAIN, and see if they update the BIOS or find out the true problem. I prefer to be the BIOS or a motherboard design flaw, because this way I get everything working again in the same day, but in case the mobo died somewhere (which I really start to doubt since it only reboots at certain specific programs and websites), I am screwed for a month or more.
So what do you think? Still a screwed mobo, or just a CMOS/BIOS waiting to be updated/flashed?
I also made all sort of tests to viruses, but since I reinstalled windows it still happens.
CPU: Intel Dual-Core E2160 (1,8 GHz)
RAM: 2x1024Mb DDR2
Mobo: ASUS P5PL2-E
GCards: My ASUS nVidia 7300GS fried, so they gave me an ATI Radeon (where the restarts started) then yesterday they gave me a new one, which I am currently using: nVidia 7300GT Silent
HDs: 160Gb SATA (3 partitions) + 160Gb IDE
OS: Windows XP Pro SP2
EDIT: It started to reboot at forums sites as well with FireFox. Going to use IE only for now to see what happens.