CPU still running hot after Heatsink change

[rhydiansmith]

I bought an old PC from a friend and noticed it would turn off after about 2 minutes every time i turned it on
I went into the Bios and saw that the CPU was at 70C. I thought this was the cause of the problem so I bought a different heatsink
After fitting and applying new thermal paste the new heatsink and turning it back on, it would still turn off after about 2 minutes, so I went back in to the BIOS and it was still running at 70C!
Can anyone tell me why its still running so hot and maybe why it keeps turning off?
Thanks

 

[popatim]

Are all the fans spinning?
How much thermal paste did you use?
Whats the temp if you run it with the cover off?

 

[twelve25]

IS the new heatsink actually a better one?

 

[satyamdubey]

first things first: system specs?
If its an AMD, then 70C is way too hot indeed. If its Intel its just hot but not extreme.
there is a good chance that the old PC has a dying/degraded psu.