My PC lags badly after leaving alone running for a While? Help!!!

Hello SevenForums, I need your help. I am running Windows 7 Ultimate 64bit on my PC

Its a Dell Inspiron
Core2Quad core
4G RAM
AMDRadeon HD (I don't which one exactly)

Though I rebooted my System a few days ago and it all was fine. Now if I have it running and i leave it for a few minutes (15-30min to an hour) when I come back and move and mouse everything in the computer gets super slow, its absolutely ridiculous!!! I get to the point were I shut my PC off and turn back on so that it stops that. This happens every time I leave the PC. If im working on it actively its fine but when i leave and come back its just terrible the computer is super slow and takes forever to open and close anything, the mouse also freezes and moves(major lagging!!!). Please help me !!!!!! How can i fix this problem????

It started yesterday after i rebooted it, I left for 30 min and came back and the PC lagged ridiculously, now i cant leave for too long otherwise it will do that. I had this for a few years but i don't know exactly how long.

Ok here are all the updates i did so far....
















these should all the updates!!

This picture i took the moment you asked for the TskMngr



as you can see the RAM usage is already high, and im not running any big programs

this is after 5-6mins after leaving the PC alone with no extra programs on.



as you can see here the RAM usage is way to high and I begin to lag. I don't know what going on????

Work through these troubleshooting steps starting with running a completely Clean boot - add your AV back in later after seeing if it is the problem.

This is the RAM usage if every program is off