Most likely you installed something and whatever that is waiting for the, now missing resource, to become available, so it waits-and-waits-and-waits until it times out. Recommend going back to a, known-to-be-good, restore point.
I had a similar problem with my Plextor. It turned out, that when the disk usage is > 90%, the disk becomes significantly slower. What I did was to remove the old Windows restore points, by shrinking the space available for windows restore to 5% of the disk space. This resolved the issue for me, hope will help you too...