Loading Application Problem on Win98SE

I have 2 computers with exact same problem. Both computer are running Win98Se. Previously both computer were running error free on all applications. Suddenly most Windows applications will not load up. Some Windows features such system properties, or any feature under control panel will not load up. I scanned for Virus with Norton AntiVirus 2003 and it found no virus. I re-installed Win98Se and yet problem remained same. I do not want to re-format hard drive until I find no more solution to above problem.

What are the possible solutions to my problem?