So today I upgraded my brother's Celeron 633 to a P3 733 (sorry for being so dated ;) and now I get random BSODs/restarts whenever I'm doing something memory intensive. Normally I'd suspect bad memory or overheating with a problem like this, but the system is definitely not overheating, and I'm reluctant to suspect the memory for two reasons: 1. The mobo I'm using is an MS-6312 based on the Intel 810e chipset. I've heard that the memory is always locked at 100MHz with this chipset (not sure of this though). Likewise, even though the FSB went from 66MHz with the Celeron to 133MHz with the P3, I believe the memory is still running at the same speed. Can anyone attest to this, or was the memory actually running at 66MHz before and 100MHz now (I know the 810e doesn't support 133MHz memory and unfortunately no utility is able to determine the mem bus speed on this computer)? Regardless, both DIMMs are PC100, so I don't see a problem here. 2. With the Celeron, I ran the system weeks on end without restarting and never had any problems, so I'm quite sure the memory is good. The problem only occurs when using apps with large datasets like games, and these sorts of apps don't last a minute before they crash. With casual use, the system seems quite stable (I'm writing this post on it now, for example). I've tried testing with three seperate DIMMs independently and the problem did not go away. I'd be willing to buy more RAM if I thought it would fix the problem, but I don't think it would. I'd hate to think the CPU is actually defective, but I don't know what else to suspect. Btw, the BIOS offers no options whatsoever for adjusting memory settings. Any ideas?

Have you tried running Memtest86? http://www.memtest86.com Let it run a few loops and see how you go. Completely useless? I can always be used as a bad example

Also check the vcore and have a go at downclocking the FSB to 100MHz. Completely useless? I can always be used as a bad example. There are 10 types of people in the world. Those that understand binary, and those that don't.

What is your power supply wattage? You may need a new power supply that can supply enough power to the new chip.

I did run a memory tester (in windows), but it would just crash to a BSOD before it would report any errors. I should've known better than to "test" the memory in Windows, so I'll try Memtest86 in DOS and see what happens. As for the Vcore and FSB options, I have no control over that at all with this mobo. The only jumper on the board is to clear the CMOS and in the BIOS the only "Advanced Chipset" option is PCI latency, of all things. The power supply is 300W, but it's really cheap. I'm running my loaded AthlonXP system on a 300W PS with no problems, so although the PS *should* be sufficient, I'll try another PS and report back. Thanks everyone.

Well I tried Memtest86 (the bootable version) and it consistently freezes at random points early in Test #2 of 9. Up until that point, however, it does not report any errors. I also tried another 300W power supply and the problem still exists. I already have the latest BIOS version and there's no installable chipset driver for this mobo, so I think I've covered almost every angle. I've already poured many hours into trying to fix this, and at this point, I think I'll just cut my losses ($20 ;) and put the old CPU back in. Besides, I really should upgrade the whole platform to something a bit more modern if I want to see any appreciable performance gains. Thanks again for your suggestions.