I'll keep this one short, My girlfriend is on her second laptop were as i'm still on my first. She has an ASUS (i'm not sure of the model) and she's always leaving it on the floor next to the bed and falling asleep with it on her knee so it's been dropped once or twice. She's only just told me about this but when ever she tries to type using the built in keyboard extra letter are added, caps lock is turned on etc.
I have used the on-screen keyboard and a USB keyboard without any issues so would i be right in thinking the built in keyboard needs replacing ?
Alrightio, my guess would be the internal keyboard too. Check if any of the keys on the keyboard are stuck, that might play a big part. Other than that, I can't think of anything but the keyboard itself. Depending on the model, it shouldn't be that hard to replace, you just gotta keep track of the screws ;)