best to do a defrag in safe mode, windows is using less files so theres more of them avalible to be defraged.... plus turn off disk caching while you do it
(right click my computer/properties/advanced/preformance/advanced)
not that that will help you much at the mo...
Id still swap around the memory first just to double chck its not that, just try with one stick... ok your computer will be a bit slower for 5 min, but its just while you test it
tho as youve tried the old stuff back in anyway, Id say go for a format