Very, very strange problem!

[problem]

Hi!

Since I upgraded my PC from Intel E4500(OC'd), 3GB DDR2, and ASUS P5B-E to i5 2500K (no OC), 8GB DDR3, and ASUS P8P67Pro my computer has started to shut down (hard reboot, w/o BSOD) when I use anything graphic card related. For example, the computer works flawless in Safe Mode where I can surf and watch videos for hours, but I soon as I enter normal mode and watch a video, start a computer game, or surf with GPU acceleration, it turns off.

I've reinstalled Windows, changed HDD, run Memtest86+ for 12h w/o errors, used one memory stick, changed motherboard, and underclocked my CPU. Nothing works and I wonder if you guys think the reason is my PSU (Antec Smartpower 2.0 450W ~3y old), or my graphic card (HD4830, oddly use with the same PSU in my pre-upgrade system)?

Thanks

[HFat]

A driver issue perhaps? Do you have access to the driver version you used before upgrading?

If it something like the RAM or overheating, it would happen in safe mode.

[Deucal]

I presume you have a windows 64bit(needed for the amount of RAM you have) and that you have the current driver for that version of windows and not a 32bit gfx card driver version.

are you using default windows drivers, the one from the manufacturer or the ATI website?

[murtoz]

Hard shutdowns like this are typically initiated by the PSU (it actually taps into the shut down signalling so is one of the few devices that can do this). This is normally the case if there is an overcurrent situation where the PSU shuts the system down rather than allowing damage to occur.
This doesn't mean the PSU is the cause of the issue though, it could be a faulty graphics card or a dodgy connection. Reseating all components and cables is a good first step (particularly those to the graphics card). Cross testing is the next step. It seems unlikely that your components would overload the PSU so something faulty (3d circuitry on the graphics card?) would be my guess.
Good luck!