Problems with input from keyboard and scroll wheel?

[#1]

My PC has developed a strange problem. I can be typing into a text window (like this one or Notepad) and suddenly my input stops appearing and I hear a tinny tone for each key press. I notice that the colour at the top of the window goes paler as this happens. Also if I am scrolling down a list on screen using the scroll wheel on the mouse it stops responding. The mouse pointer continues to move OK.
This is happening roughly every 50 seconds. I can restore input simply by left-clicking but then it will recur 50 secs. later. My keyboard is wired PS2 but I have a wireless mouse. I'm using Windows 7 64 bit.
Can anyone offer a solution.

[#2]

It sounds like there's another process running that is grabbing focus away from what you're doing.
You'll need to check what processes are running to see if there's a likely culprit (especially if you've installed something recently), and do a malware and virus scan

[#3]

Good morning,
This is usually caused by an issue with a windows system file (the actual name escapes me but a google search would uncover it.) SFC /scannow command will recover but I believe you should do run it while booting from an installation disk so that your operating system isn't currently loading. If this is a problem there may be an option to run the scan, restart and run the scan again pre-loading.
full details can be found here (3rd party site but safe and reliable)
http://www.sevenforums.com/tutorials/1538-sfc-scannow-command-system-file-checker.html
Hope that helps
Twills.

[#4]

Quote from: Twills

SFC /scannow command will recover but I believe you should do run it while booting from an installation disk so that your operating system isn't currently loading. If this is a problem there may be an option to run the scan, restart and run the scan again pre-loading. full details can be found here (3rd party site but safe and reliable) http://www.sevenforums.com/tutorials/1538-sfc-scannow-command-system-file-checker.html Hope that helps Twills.

Thanks for that.
I don't have an installation disc, and I'm afraid the instructions for the second option are beyond my expertise.
I tried running sfc /scannow from a command prompt (as admin) and this did not produce a cure.