I work in Mac OS9 and the start up disc seems to be faltering?

The computer report says the First Aid cannot fix the start up disc. When I try to open the Harddrive on the desk top by double clicking the Mac freezes and I have to restart. I can open Quark and Photoshop but not Freehand. When it comes to opening this appication the report sys "not enough memory". Really weird. Do I have to buy disc doctor or something. This all happened when I opened a message from my Yahoo email. I thought Macs were basically immune to most if all viruses. If anyone can give advice this would be great! Ta, Gman