So my system has an i3-3550, using integrated graphics in Windows 7 64 bit. Generally, the system is stable, can run cpu exercisers without issue and video playback works great with and without DxVA in use. xbmc's OpenGL seems to be accomodated easily enough.
However, if I run pretty much any Direct3D game title (tried Portal 2, CoD:MW2, Sins of a Solar Empire), the system locks hard in fairly short order. Keyboard LEDs don't respond, last audio sample endlessly loops. In fullscreen or windowed the lockup occurs (in which case mouse cursor stops responding even if the cursor is outside the application), and hard power cycle is my only remedy. I wouldn't have been surprised by very low performance from the HD2500, but I didn't expect it to hard lock the system.
I tried various things, just one 4GB dimm, then the other, disabled RC6, disabled VT, upped the RAM reserved for the GPU, disabled DWM. The symptom stayed the same. MW2 gets the farthest, not locking up in the menu, only when actually trying to render gameplay. At 1024x768 it actually lasts a few seconds before locking up even. 1280x720 can't render a single frame. Portal 2 menu always locks up when trying to render an effect where the backdrop gets flipped square by square.
have you tried updating the bios for the motherboard?