RS480M2 - No boot after replacing RAM

Question

A pair of RAM sticks originally installed in the slot 1 and 2 were DDR400 2x256MB with 3-3-3-8. Then before installing Vistax86 a new pair being DDR400 2x512MB 2-2-2-6 were installed in the slot 3 and 4. Everything appeared working fine except cpu-z indicated that running speed of the RAM changed from 200MHz 3-3-3-8 to 133MHz 2-2-2-6. The PC was a triple boot system for W2K/WXP/Vistax86.
After one year later this time around, the original RAM pair of 2x256MB were removed and the pair which were later added as above were moved to the slot 1 and 2.  After this change of RAM any one of the OSes failed to boot. Error message on each OS as follows:
On WXP x86:
Windows could not start  because the following file is missing or corrupt
<Windows root>\Sysem32\ config\system
On W2K:
Windows could not start  because the following file is missing or corrupt
<Windows root>\Sysem32\ ntoskrnl.exe.
On Vista x86:
The system failed to boot and a long error message was returned which said something to the effect that the boot failure was caused by recent hardware change and signature was not recognized.
The message included recommendation that the system is let boot  from the Vista setup disc and select "Repair" , so I attempted to do so but the system failed to boot from the disc and instead the same error message as above was returned.
Why the system became incapacitated to boot?
This is not about my own PC: Disregard my signature.

Answer 1

"As to the psu, I understand your comments. But the system has been stable for three years running WXP with 256MBx2 at 200MHz 3-3-3-8, and the last one year running Vista with 512MBx2 added. Since this RAM was added the operating memory frequency and the CAS latency were changed to 133MHz and 2-2-2-6 with BIOS setting for AUTO. What I am trying to do now is to see if there is a way to improve the sluggishness of Vista operation."
One more reason PSU to be suspected.{3 years old cheap PSU}
I can set it only as CL=XX in combination with a memory frequency. The combinations so far tried are 200MHz/CL=2
Why you are tested so tight timings?!
Leave them to Auto and re-test, else:
You can apply any CL value without the matter of the memory freq.
About other timings you have "Timing Mode" switch it to manual. Then input other timings.
"Since these sticks are used for dual channel mode, I have tested the two sticks(DDR400 512MBx2) together."
Test each one of them individually, some of them can be defective...
P.S: That's my last comment in this topic, i'm bored to repeat the same tips xx times in each reply and you do no action, but discuss theory.