if it is overheating, then your fan may have failed. Also, try replacing the thermal paste on the CPU.
Also, that isn't all that slow, as I used to have both a Intel 486 (I'm pretty sure it was one of those 66/33 MHz CPUs), and I had whatever came in those old XT computers (had to look this one up. It had a 4.77 MHz processor and a 10MB HDD ).