Virus trouble

I have two pc’s linked with a software interface only these are not Networked i received a virus through emails and did not hav protection on my systems. 1st pc was under warranty RTB and returned ok but company would not repair my other.
I therefore installed Norton’s 2002 on my second PC which has Windows 98, but program wont run my systems running slow with intermittent application errors and when i shutdown for say 1 hour then re-boot alls ok for a while.
I have important data on my system also so i would appreciate an safe and effective solution from someone who can help me.

Kind regards Bill