Question Fast computer is sometimes slow with not responding programs at all

[OmbcMax]

I've normally a quite fast computer with

• 256GB m.2 SSD (with windows 10 on it)
• 3000GB HDD
• CPU i5820K @ 3.30Ghz
• GPU GTX 970
• RAM 16 GB

So the weird thing is that sometimes when i boot my computer the computer itself starts really fast. Then once in windows it begins to run my programs.
And in case you say stop programs that start when your boots. Nope i want them to run since i will be using them all day!

And if i restart the super slow not responding computer wich by the way takes for ages because its so slow.
Then when my computer is restarted its super fast it launches everything in some seconds and everything is just responding fine!

I have good antivirus software (ESET) and i dont think that is the problem since it is sometimes the case not always...
And im quite experienced with computers so the basic clean your cache and uninstall some programs wont do the job...

Also worth noticing is that my task manager is quite doing alot when my pc is fast and is almost doing nothing when my pc is slow... Almost as if its on like a power save modus while its a desktop pc running on full performance modus!

Could anyone help? Thanks!

 

[rgd1101]

make and model of the psu?
check cpu temp when it is slow?
malware scan?

 

[OmbcMax]

Nope neither of these... what do you mean by make and model?

 

[OmbcMax]

?