Hi I have an acer aspire 1 series NAV50 some of the keys on the keypads not working.Could you help me rectify the problem?

I had this problem too when I was putting in more ram (i had to take it apart...) and then certain keys didn't work. Here's how I fixed it:
1. Disconnect all power supplies
2. take apart your computer carefully as if you were to put in new ram
3. when you disconnect your keyboard, blow on the cable you detach to get off the dust
4. blow on the system itself so that there will be no dust.

That's basically what fixed it for me... I hope this works for you!