That’s terrible! Or perhaps, out of sympathy, I should type “ha’s errible!”
Luckily, you may be able to fix the problem with a cleaning:
Shut down the PC. If it’s a laptop, unplug it as well, but leave it open. Turn the keyboard–or the open laptop–over, and gently tap the back. If it’s a laptop, be very, very gentle.
Concentrate, of course, on the dead keys. Put the keyboard or laptop down, right-side-up.
Use a can of compressed air to spray out any dust between the keys. You can buy such a can at any computer store; I’ve seen them on sale online for as little as $3. They always come with a thin straw. Use that to direct the air between the keys.
If you have a desktop, you can also untwist a paperclip, and carefully use it to pry out dirt. But that’s too dangerous for a laptop, where the keyboard probably sits on other, more important electronics.
If a cleaning doesn’t help, you’ll have to repair or replace the keyboard. If you have a desktop, just replace it. External keyboards don’t cost much (some cost less than $10), and are easy to install.
But laptop keyboards are difficult and expensive to repair or replace. Unless you’re extremely comfortable working with tiny, closely-packed circuitry, I strongly recommend bringing your laptop to a professional.
There is one other option for laptop users: Buy an external keyboard. Some of them, like the Goldtouch Go! Travel Keyboard, are quite small and designed for easy carrying. Your laptop will lose some portability, but not all of it.