Complete:

If you have a virus on your computer, all your files and documents are in danger. You should install an anti-virus programme.

If you cannot connect to the internet, you should phone your internet provider and report your problem.

If you've spilt something on the keyboard, you shouldn't use it for a few hours.

If the screen is frozen, you should restart your computer.

If you have deleted a file by mistake, you have to / will have to ask an IT specialist for help.