Keypad problem of sony ericsson
It could be any number of problems, jhoyz0018: a fault, it has been dropped, or it may just be dirt/dust that has lodged under the membrane and stops the keppad from working properly.
You have three options:
1. If you bought the phone from a store or direct from a manufacturer or Airtime Provider, return it for replacement/repair.
2. If you have Phone or Home Contents Insurance, make a claim for a new phone on that.
3. If you bought the phone second hand, off eBay or similar, then carefully remove the fascia, clean the membrane and keypad with a lint-free cloth or air-brush and re-assemble. If still not working, you will need to return your phone for repair/replacement.