Thanks for the additional info there. Bear with me, since I don't actually have a P4C800 Deluxe... I downloaded a copy of the manual and that's what I'm referring to with the following instructions. If the page numbers don't match up with your printed copy of the manual, then I apologize in advance :Q
- When the system powers on, begin tapping the Delete key on the keyboard in order to get into the motherboard's BIOS. The BIOS screen should come up with menus that you can navigate using your arrow keys and the Enter key.
- Go into the Advanced menu, and then into the JumperFree Configuration sub-menu there. This is shown in the manual in section 4.4, page 4-14.
- Set AI Overclock Tuner to Manual by selecting it, hitting Enter, using the arrow keys to select Manual, then Enter again. Now there's an additional list of items you can configure manually

- On that list, set DRAM Frequency to 400, since your memory is DDR400 aka PC3200
- Set the DDR Reference Voltage to 2.75. This is a little more than stock, and may help stabilize things.
- Now press Esc key to get back out of the Jumperfree Configuration sub-menu, so you have the Advanced menu again (shown on page 4-14).
- Go into the Chipset sub-menu. In the Chipset sub-menu, which is shown on page 4-18 of the manual, you can adjust your memory timings.
- See the following timings: DRAM CAS Latency, DRAM RAS Precharge, DRAM RAS-to-CAS Delay, and DRAM Precharge Delay (page 4-19 of the manual). Set those to 2.5, 3, 3, and 8. While you're in there, set the AGP Aperture to 128.
- One other thing you might want to do: go into the Power > Hardware Monitor menu and disable Q-Fan for now. The manual shows that on page 4-30.
Your power supply is a name-brand one, so that's a good thing. If it were me, I'd be going for more like a name-brand 400W unit or so, but I'd take your Enlight 320W over a cheesy el-cheapo 500W generic one any day.

Your 4-pin auxiliary power cable is plugged into the mobo, right?
Hang in there and try this stuff to see what happens. If that doesn't fix it, post again and there are some diagnostic programs you can try, such as
Memtest86, to see what gives.