Richard Lewis typed:
Yes, I've removed the new RAM now (and I gave all the cables a good shove while I was in there).
I get exactly the same problem.
Try reseting to BIOS defaults (first try "fail safe", then "optimised" if the options are there). Adding new memory may have caused the BIOS to alter the memory timings or something like that.
I'd strongly recommend running memtest86 (www.memtest86.com, easiest option is to download the (tiny) ISO image and boot from it to test). Run both without the new memory and with it, just to be sure the memory is OK, and make sure you run the tests at your desired memory clock speed (ie don't run the tests with BIOS "fail safe" defaults and assume they're relevant when using "optimised" settings).
It's odd that the problem remains with the new memory removed, but it's conceivable that a fault in the new memory has lead to something incorrect being written to disk which is still there after the memory is removed.
Strange behaviour like this can also be caused by an underpowered PSU (eg I've had files corrupted when transfered across a network which were fixed by upgrading the PSU; no other ill effects were noticed). Seems odd that the problem has just started, though.