I'm going to answer because I want to help you, even though your question isn't quite right for this forum.
First, make sure the heatsink is firmly seated and secured. If you can move it, then it's not attached properly. I assume there is existing thermal compound on the heatsink/CPU!
Second, check that the fan is indeed working.
Keep your PC open and power it on. If/when you can get into the BIOS, gently apply pressure to the heatsink (not the fan, but the heatsink) to see if the temp changes.
If you're still stuck at 86C (and it doesn't change at all) then I think you can be reasonably certain something is wrong at the hardware level. Note that, at 86C, the BIOS should be running the CPU fan at full speed. You should definitely notice that. If it's not running at full speed, then that's another indication that something is wrong with the hardware. At this point you could try disassemble the CPU/heatsink and reassemble with fresh thermal compound. While you're at it, re-seat the CPU (i.e. take it out of the socket, put it back in). But I wouldn't hold out much hope.
As a last point, it is very rare but definitely possible that the BIOS itself has become corrupt in some way and you're seeing the symptoms of it. Either the settings, or worse the BIOS firmware itself. You could try clear/reset the BIOS settings via whatever method your motherboard provides (usually you unplug power and short some special jumper or press a small button for a few seconds). Failing that, you could try updating BIOS firmware but that's risky if you can't guarantee your PC will stay on.
In the end it might be time to retire the PC. All PCs have a finite lifespan and you may well be witnessing the end of this PC's life.