hi had a client with a Sony Vaio with similar problem she said it was dropped as high as her knee and suddenly some keys stopped working and other key where pressed simultaneously ex. 3 and f3. Plugged in an external keyboard and all work fine, opened the laptop and nothing out of place. So pretty easy dilemma :
-undo all the keys clean all the contacts and retry it after a few hours of work
or
-replace with a new keyboard at the cost of 39.99 + labour.
guess what i did