Sony Ericsson :: C510 Software / Hardware Error

I have a C510 Sony Ericsson Phone. I bought is about 7-8 months ago. Recenly it has started behaving a little weird. I couldn't figure out if it is a software problem or hardware problem. Some of the problems it is showing are:It is very slow. Actions take place after 5-10 seconds after pressing the keys. For example: To look for a name in PhoneBook, if I type 'R' after 5-10 seconds it will show names starting with 'R'. If I press the Dial button on some contact, the phone hangs (the screen also goes blank) until the other party picks up the phone.Sometimes the screen splits up in two identical sub-screens. Restarting the phone is the only options in this case.This is what I did to fix it:Formatted the memory card after backing up the essensital data (contacts and notes)When the above didn't work I did a Master Reset The phone got a little (very little) faster, But No significant improvement. This tells me that the problem is not software related. There is some problem in the hardware. Let me know what to do. today It showed a new problem: "While searching in the phone book If I have to look for a name say "Prashant", and to start with I press key '7' to type 'P', it types direclty the third letter on key '7' that is 'R'. And the name starting with 'R' show up. The same thing happened with every key (1 to 9). " I restarted the phone and it got back to normal. This is getting irritating. Tell me what can I do.