Perhaps you accidentally didn't plug in the cables or something properly? I've heard of cases like this happening where the cable wasn't pushed in properly and the printer is not recognised. And make sure you have the latest drivers and so on for you printer... sometimes that could also be a problem.

You can also try to view if Windows detects your printer by going to Start > Control Panel > Printers and Other Hardware >View installed Printers and Faxes and try and see if you can see if your printer is installed correctly. If not you can also try the Add Printer Wizard (Start > Control Panel > Printers and Other Hardware > Add a Printer). Hopefully you can make use your printer after this. You can also try System Restore (All Programs > Accessories > System Tools > System Restore) and try to see if your printer works with a configuration that you had before, but I don't recommend this because this could cause other problems.