When you checked your TIM, you re-apply it when re-seated the heatsink??..
Like AMDforME said, and I share that same opinion, it seems that the cooler isn't seated properly. There's no way ANY cpu could rise temps that fast when everything is supposed to be properly installed and/or working well..
Since you said that everything were okey for about a year, and then, suddenly, your system started to behave like that, then maybe there's something wrong.. But, without any other relevant info about your system specs, it's hard to tell..
Could be the PSU, could be the mobo and/or circuitry, could be the cpu heatsink fan(s)..
Please, fill the info as the STICKY said, and then maybe we could bring you more help...
8320 @ 4,7 / 990FXA UD5 / 7950 @ 1100-6000 / Switch 810 / H110 p-p / 16 GB RAM / 23" 5760x1080 / SSD 64GB RAID0 / HX750 / SB Recon3D Fatal1ty Champion / z506