I have a fairly new homemade PC and I've been having a lot of things go wrong with it.
Just recently, I had to replace the motherboard (ASUS K8N-VM) because the old one didn't have a functioning PCIe slot. The replacement is the exact same make of board as the old one.

After I replaced the motherboard I was having problems with the memory (or that was what asus support told me) because the computer was crashing as soon as I tried to run any programs. I was told by asus support to set the ram speeds manually, and I did, which seemed to help. but then it got worse.

Right now the computer crashes whenever I try to boot up, before I get to the desktop. I did a completely fresh install of windows 2000 and I ended up on the desktop, but when I put in the motherboard drivers (ethernet, sound, etc) and restarted I was unable to get to the desktop. This isn't a problem if I boot up is safe mode, but it is a problem even if I use another harddrive. I've checked the cpu temp in the bios after a crash and it is usually around 39 C (80 F), so I don't think it is that.

Is this still a memory problem?
Does anyone have any other suggestions?

Is your power supply putting out enough juice?. Use the exact wattage of each of the componets in your system. Add them up, see if the supply can handle that. Or use the following estimates:

Part Juice needed (watts)
Motherboard 15-30
Low-End CPU 20-50
Mid To High-End CPU 40-100
RAM 7 per 128MB
PCI Add-In Card 5
Low To Mid-Range Graphics 20-60
High-End Graphics 60-100
IDE Hard Drive 10-30
Optical Drives 10-25