My PC went so slow its unusable

[granli.john]

My computer has been working perfectly fine for 2 years. One evening i was playing and i decided to open up a game i hadnt played for over half a year. After i got into the game i took the game in windowed mode and then my pc froze in intervals of 20 seconds freeze and 5 seconds working. I restarted my computer and now it is like what i just described. When i try to open programs it takes 5-10 times longer than usual and all programs i try to open crash because of the slow PC. The game i opened and took in windowed mode was The Long Dark on Steam.

 

[rgd1101]

check cpu temp?
check hdd health?

Ran malware/virus scan?