No, do not remove SP1a. Does your PC have USB2.0 ports...it is a HP USB
printer you're referring to right? (You're not giving us much to go on with
your question!)
If the printer is not being 'found' then it's the USB drivers, NOT the
printer that is causing the problem... You may have to unisntall and
reinstall the USB ports.
I have this same problem. My USB ports (and hence my HP
PSC2110 printer) seem to have stopped working since I
installed SP1. How does one reinstall the USB ports or
port drivers?