Which email client are you using? Webmail? Microsoft Outlook? Outlook Express? Thunderbird? Eudora? Incredimail? Something else?
Can you type things in any other type of program, say a text document or Microsoft Word?
What type of operating system is installed on the computer?
Laptop or desktop?
What type of internet connection?
Have you tried swapping in a known "good" keyboard?
The more information you give us, the better informed our answer will be.
Hope this helps.
I cannot reply to emails because when I endeavour to reply and commence typing, absolutely nothing comes out to show what I have typed, apart from a thin yellow line.
Can anyone out there help me please.