Win 98 system locks up and reboots both

The computer had files infected with Magistr, supposedly repaired via norton from another system. Also the system has had a history of cpu fan not working (thermal issue).

CPU and memory has been changed and since the system is running tremendously better. The system use to lock up and reboot quickly, now it takes sometimes hours, but still either locks up or reboots on its own.

Do you think a slick and reload should fix this?

Thank you for your assistance.

RWH