Windows 7 Performance issue - slows down after a couple minutes of use

Hello,

I seem to have the same problem as was solved on the following thread:
Win7 works smoothly, then Suddenly slows down.

My computer boots up fine and quickly, then works for a couple of minutes as normal but then slows down to an unusable speed.

I ran Speccy and my graphics card does not seem to be running too hot so I figure it must be something else (see screenshot below). I have just done a fresh reinstallation of the operating system and have McAfee running. I ran a clean boot (How to perform a clean boot to troubleshoot a problem in Windows Vista, Windows 7, or Windows 8) and the problem was still there.

A further problem is that when I press Ctl+Alt+Delete I get an error message as follows:

Failure to display security and shut down options. The logon process was unable to display security and logon options when CTRL+ALT+DELETE was pressed. If the operating system does not respond, press ESC or restart the computer by using the power switch.

Any help would be greatly appreciated!

look at this: Failure to display security and shut down options. The logon process - Microsoft Community

also scan your pc with an anti-virus. I suggest you to download and install Microsoft Security Essentials.

try also to restore your computer with a system restore point.

I came across that site and thread already and tried it out, unfortunately none of the solutions worked for me.

I have McAfee installed and have had no problems with it in the past. I will install Microsfot Security Essentials and see if that does anything.

I have only just reinstalled the OS to try and fix this issue, and immediately after the re-install my system was behaving the same as before. Hence, there will be no restore points for me to restore to. Could it be something to do with dust? I saw that on another thread about Blue Screen of Death, but my issue seems different as I do not get BSOD.

This might help