Why do the fps moving up and down sometimes.

Started to play again after a year without playing. Then when i play my fps can be god but after some time the fps moving up and down and i cant play, cant hit and its lagging. What to do ??
Thanks for help =)

T.M.T SWDEN

Well if it was good before you took your brake i would say that your PC/GFX is overheating coz of dust and all messy things that colected inside during that time ^^ At begining i can give you advice to open your box and clean it out a bit (mostly radiators) it worked fine for me

Overheating would be my guess also. Open up your PC and remove all the dust with compressed air / vacuum cleaner. first one is better imo

Thanks for the suggestions =)
Then waht to do when i have a laptop i´m playing on ? Buy a colingboard for it ??

If it laptop i am sure its overheating xD have same problem Coolingboard will help just for a while (if it helps at all) best option is giving it for cleaning to some service since it doasnt take too long. But for playing coolingboard is always a good option