I must have misread your psot a bit. So you're saying after changing the timings, your pc worked perfectly until just recently?
Hmmm... are you changing the DRAM voltage? Make sure it's getting enough power for the timings/frequency you're pushing into it. Anddon't forget a 1:1 FSB
RAM ratio, or close to it can help If you OCed the CPU to 2.6Ghz, but didnt increase the RAM speed, then your RAM is transferring stuff too slowly to take 100% advantage of your CPU's speed. Make sure the CPU is getting enough voltage too.
I'm trying to think of other settings that could change things... Do you still have the RAM packaging? I'd like to know the "default stock" speed, timings, CAS Latency, etc.