How to make scanner compatable

I have a Demension 5150 with Pro XP and HP Scanjet 4200C with USB connect. When I first install the scanner program everything is fine for one or two scans then I get message saying Can't locate hardware or hardware not connected. If I delate the scanner and reinstall the connections and prorgram again I may get another scan but the same thing happens. Oh I forgot to mention before I installed scanner I ordered an updated drive from HP (2006) and installed. Please can someone help? My work is backing up. Is their a MS drive that can be substituted?

Thanks