Well, again, setting tRAS too high will not buy you anything either. The rule of thumb is: tRAS= tRCD+CL+2 (or +3). This way you have all your parameters matched up and working with each other instead of against each other.

If you set tRAS too long, it shouldn't have too much of an effect, except for unnecessary delays of the page closing in case of a single burst transfer. I don't see how this could mess up Windows, most likely, you have some "creeping corruption" from your earlier tRAS=4 settings somewhere.

see: http://www.lostcircuits.com/advice/bios2/7.shtml

My recommendation is to reformat your drive and start clean.