I had this problem the other day. If you have replaced the actual hard drive, you may need to install a legacy version of intel rapid storage technology driver. I did the whole banana; renaming software distribution folder stopped and started all the WU services you name it.
The intel rst did the trick. BTW I manage our WSUS at work for about 1K clients. WSUS is very temperamental so I wouldnt recommend it unless you are using AD w group policy.
What is this "Intel RST" you mentioned? I don't know that I'm familiar with that.