Portable Hard drive problems

My computer has Windows XP Home addition operating system installed. The installed hard drive is a 80 GB Seagate. My two External Hard drives are 250 GB Western Digitals. I recently had a virus problem with my PC and decided to reformat my C drive and reloaded my operating system from the provided disc. When I was complete my two externals weren't readable anymore. I mean the computer saw them as mass storage devices, but when I click on them it wants me to reformat them. Does anyone know a fix for this? I have tried them on other computers and get the same reformat answer.