3 Possibilities:
1. Your Termal Paste is overaged and became brittle. In that case you'll have to change it.
2. Your case or at least your cooler being dusty, clogging the thin space in between the cooling fins and thus not letting pass as much air as before and heat building up in your case. If it's just your CPU and not your GPU toon however, then it's probably not the case. A tourough cleaning of the entire case should solve your problem then.
3. Your CPU fan being clogged or rotating at lower speed than normally, reducing it's effectivity. If it's the former, just need to clean it up. If it's the latter however, then something's up either with the fan or it's power supply on the Mainboard and might need to replace one or even both of them.







