Im having a Odd problems after my PC idle for hours?

i have Windows 7 retail Ultimate and im using 64bit with SP1 and my major problems after i resume my computer that Idle for 1 to 3 hours i get (i usual leave my computer when i download some files or compressing a massive huge files)

1.i can't use or open TaskManager or pressing CTRL+ALT+DEL wont work

2.i can't install any programs or applications at near end of installation i get a error says that my temp folder have something to do with it

3.i can't extract a zip/rar or any compressed files i get the same error in #2 it says about temp folder or some file is missing

4.in Firefox (and other internet browsers) i can't download anything when you download something the download manager of firefox wont pop out and or any download progress

but after my PC restarted or rebooted all these problems are gone and back to normal i dont think i have a virus or something i already full scan my computer 2x with various anti-viruses and malewares after experiencing what happen the result is Clean so far and my HardDisk? i dont think their dying...i even turn off the "Turn off hard disk after" features in power setting still didn't fix my issue... so anyone here knows whats happening to my PC? there could be anyone here experiencing the same thing and fixed it?

Probably the problem is due to excessive junk. Please clean all the junk files and the Registry using CCleaner or any other program that you use and then try doing what you were unable to do earlier.