Nope not trollin...askin seriously cus for some reason no matter what setting i have it on it stops playing after so long
You have another issue than. You need to be real spesific so we can help you out with your issue. If the GPU is in working order it will be fine. Have you installed the latest drivers for you GPU ?
I know the 9400 is old and a little on the weak side, but I'm pretty sure it can at least run 720p videos just fine. I had an old single core athlon 64/9500 gt playing youtube videos just fine at 720p a few years ago. So I'm inclined to agree that there is something else going on. Would you mind listing other parts in your computer? My gut feeling is that it is either the driver or cpu.