how can i fix the upper keys?

i have a problem with my u600 phone. i can't use the upper keys (cursor keys and the soft touch keys) except the power key ha! i thought that it's just a problem because maybe, my battery is weak. so i tried to use my friends newer 3.7V Li-ion battery, just same with mine. but unfortunately, there's no changes. it's just the same problem. i hope you can give an idea how to fix my phone aside from asking the company or returning it to the shop. thank you very much and more power!