If a program or window on your PC seems to have frozen up and you cannot close it by clicking the X (Close) button in the top-right corner, hold down the CTRL and ALT keys together and tap DELETE once.

In Windows Task Manager click on Applications which shows all the programs that are currently running. You can usually tell which program has frozen or crashed as its Status will appear as Not responding. Click to highlight that program on the list then click on End Task. The PC will now attempt to close it. If it is successful you can then close Task Manager and the PC should be able to carry on as normal.

If Task Manager does not appear, try holding down CTRL, ALT and DELETE and keeping all three keys held. This will restart your PC, which will often fix the problem. If these keys don't work, you will have to press and hold the power switch or turn the plug off. Turn the PC back on. Your PC should be alright but always try to avoid switching off without shutting down properly first.