There may be two seperate issues here. Existing in place memory fails because it is damaged by a power surge, BUT there is also a separate issue with recognition of new memory. Getting it to boot after changing sticks and slots is pot luck - but once a configuration is accepted and boots it will boot from cold (at least until the next powerr surge maybe). This suggests some issue with recognition? When I took out 1 of 2 working 512MB it would not boot even though i had just removed one stick that at that time was known to be working (was clearing slots for upgrade). had to move to different slots from the previously working configuration to get it to boot with memory known to work.
i don't know computers but a little about electrical, u may have an intermittent short in the female sockets that your memory chips plug into,reason for that deduction is that those are the circuits you have wiggled or disturbed and found different results,ask your computer guy how hard and expensive it would be to replace those slots, when that happens in a house you can usually pull the socket and see where the screws are lose where the wires are attached to the socket
Once you have tried: - changing bios - removing battery - getting rid of all the cards and connections to "extra bits" - starting with minimum (pref different) ram and its still there then the chances are its physical. Most likely a crack in the cpu to memory path which, when the board is warm is closed, but when the board is cold is highly suspect. Time to spend $100 on a new MB.
re: bigdavediode and kiwi's points. In the 80's when cable tv was coming on strong I put high end sony tv's in the house, all of them in a fairly short period of time had the screens go red after being on for awhile. The repair guy said it was " cold solder joints" , a result of power surges. We put a tester on the house and the overnight surges were outrageous. I installed a whole house surge protector. Never had a problem with the tv's after. This business of your ac power surging is important and low end surge protectors don't work well. edit: the best protectors/ battery units generate " conditioned" power.
I can attest to both the tv part and the cheap surge protector part as I have had a surge go right through the protector (protector never broke the circuit) and passed right through and fried my supply. That being said, again supplies have regulators although it's possible for a spike to travel through the supply lines.
Mokwit, If you haven't bought a new board yet could you detail (again, sorry) ALL of the steps you've taken to attempt to resolve this problem?
Kiwi, about to go on a trip, will detail when I get back. If I could be reasonably sure it was mainboard (what else could it be?) Power is presumably fine (changed to uprated PS), memory is presumably fine (each stick individually works), CPU runs 24/7, this would be the most time/cost effective resolution attempt. To quote Intel: "If the problem occurs even after removing the non-essential components, the problem has to be with the desktop board, power supply, memory or processor" Have removed non essential components, and seemingly (seemingly) eliminated CPU, RAM, PS that just leaves MB As ststed previously I think that there are two problems here. Having worked fine for a couple of years it stops booting because there is power surge damage to RAM, but there is also a problem with recognition of configuration of old ram or new RAM. To solve the problem the second time all that was required to restore boot was to remove RAm stick. However when I moved a stick of Old RAM a couple of months later it would not boot - booted randomly after I randomly shifted RAM around - pretty much how we solved it first time.
one other idea. If you suspect an arc or short on the RAM slot pins, from the power surge, you can probe adjacent pins with a thin probe and a digital ohmmeter that beeps (very easy to do). Then check for opens between RAM slot and bottom of the board. If you have the time, it's fast to check. ps make sure power is off when testing.