Keyboard problem

Hello,
I have a few keys on my Toshiba that have stopped working. Specifically, C, D, and R of the arrows. I was typing a paper yesterday and all was going well, at some point these keys stopped working. At times the space bar & enter key needed multiple hits to work. I thought it was an issue with Word, but the same keys do not work in any other applications. I removed every key from the board and tried to clean around them w/condensed air etc. But so far, nothing has worked. Please help!
Thanks!