if the overheating might have damaged anything else,
No or the PC would no longer be working overheated CPU or PSU would likely cause terminal failure.
a loud noise every time it is switched on
is this a loud whirring? could be fan running fast and then slows right down after a few seconds? if so is normal.
Do you mean shuts down or just freezes?
1. Overheat due to faulty / blocked fans
2. PSU voltages
3. Household power surges fridge etc switching on/off
4. faulty memory stick try memtest click here
5. virus or spyware scan for both especially if shutting down with in a few minutes of switch on or internet use
6. driver conflicts especially grahics cards get the latest drivers for your equipment