System Freezes or Reboots and sometimes won't even boot

[Brazooka]

I'll try to make it as brief as possible,

My specs first:
Athlon XP 3200+ 2.2Ghz
K7N2 Delta2 Platinum edition
3 X Kingston 512K pc3200 DDR 400
ATI Radeon 9800 Pro
Samsung 120 Gb HD 7200rpm
Seagate 40 Gb HD 7200rpm (slave)
WinXP SP2

I used to have a K7N2 Delta, bought the third Kingston 512K pc3200 DDR 400 stick for my comp. Tried to run HL2 to see if everything was good(used to have "memory could not be read" error, fixed at the time by setting my mem timings from 3 3 3 8 to 2.5 2 2 7), first time running with the three sticks: memory could not be read message. Got to the bios set CAS to 2(2 2 2 7), comp didn't boot anymore. Reset the CMOS with the mobo jumper and forgot to take the power cable off the psu(stupid, I know), fried the mobo.

Got a K7N2 Delta2 Platinum edition, defalut timings, 3 3 3 8(with the 3 sticks ), got the "memory could not be read" error in HL2 and system randomly reboots and freezes other times. Relaxed the timings to 3 3 3 10, game runs but with some stuttering and the comp wont boot sometimes, other times it freezes but no more random rebooting.


What should I do?
Is it mem timing bad setting or conflict between OS and the new mobo? Or both?
Should I format the HD?
What would be the right RAM timings based on my specs?
Is it safe to set the times back to 2.5 2 2 7?(I didn't have stability problems when using 2 512KB sticks wtih 2.5 2 2 7 and HL2 was running fine. But now, with 3 sticks with these timings, I get the memory error message)

THANKS EVERYBODY!!!