keyboard problem

I was wondering if anyone would know the solution to my keyboard problem on my 15" G4 powerbook. The problem I have is minor, but very annoying. It seems as though every time my powerbook has been idle for a bit, or even when I start it up, the first letter that I type never works. So for example, if I have left my powerbook idle for a little while and went to use it and wanted to log into MSN messenger (for example), it doesn't work because the first letter doesn't type, and what happens is that I have to retype it again. This is very, very annoying. I have had my powerbook since new about a year and a half ago and this has just started happening maybe 4 or 5 months ago. Does anyone have any solutions?