got a accer aspire 5100. when i press the letter c it types cv and when i type x i get xd. most of the other buttons work fine. do i need another keyboard?

It certainly sounds like it, BUT, if your prepared to go that route (and are aware how to do it, or are prepared to pay a shop), then trying to clear the dust etc from behind the keys "may" be worth a try, 3 ways I can think of, so 1st is to gently remove each key to clean behind them, with this there is the possibility of breaking a clip that holds them, and make sure you know where each key goes back, a photo(s) are a good idea there.
2nd is to get an old pair of tights or similar, place them over the end of a Hoover hose (this stop keys being sucked up into the Hoover), then Hoover the keyboard, with luck the suction will clear out the rubbish, and 3rd, use a can of compressed air, be warned, this is a very powerful tool, if you use it too close to the keys they will fly off, so hold it further away to start then slowly move it closer until it start taking affect but don't go closer once it's close enough to work.
Now with all these methods there is always the risk of breaking the clips to replace the keyboard (which you may still need to do as well) then it can hurt on the slim chance it cures this, but it is more probable it's time for a new keyboard, but these suggestions are free and easy to try, so can't hurt trying, hope you get it sorted.