Slow CPU

I have a Dell GX1 that has a Pentium II 400 MHz with MMX. The problem I’m having is
It’s running very slow. I reformatted the hard drive thinking that windows 98 was corrupted.. It was taking 2 hours just to install 65% of windows. I stopped the installment and took out the hard drive from out of the Dell and placed it in a different computer. Reformatted the hard drive again and reinstalled 98. It was completely done in 20 min. I can rule out the hard drive was not the problem. I’m thinking the CPU is bad.
Please help. Thank you