Its not the ram.
Its more likely the CPU fan has failed.
Open up the case, and check the following things:
Is the fan is running?
- No? Replace fan. Remember to completely clear off old heatsink compound, and replace with new compound when replacing fan.
Is it running, but so caked in dust that it can barely cool?
- Yes? Turn computer off, get a clean paintbrush and use that to clean the fan blades.
Suggest do it outside the house. Get a hairdryer and blow the rest out if possible.
Are the capacitors on the motherboard vrot?
- Capacitors are the small round things on the board. Check if any are bulging at the top. If so, you probably need to replace them.
Usually cheaper to replace the board at that point though.
Google image search for "bulging capacitor motherboard" will show you what to look for.
My money is on the fan though.