Why are some letter keys on VAIO laptop now converting to numbers?

I inherited a laptop from a Dad a few years ago. . .SONY VAIO, pretty powerful at the time. I only use it as a backup to our regular PC & laptop. It's always been a little temperamental, though, but today was just weird. Some letter keys have been "converted" into numbers. For example, the small "i" is now always a "5." What do I need to do to revert back to standard keyboard? Thanks.