How to fix my Nokia 6126?

I have a Nokia 6126 that I bought from someone because they were getting rid of it and I liked the phone when I had it. The guy I bought it from said there was something wrong with the phone and I was aware of that when I bought it as he told me in advance.

I tested it out and it keeps spazzing out sometimes it will stay still for a few seconds but then itll keep going back to the main screen and then a black screen and will altercate every few milliseconds. I was wondering if there was any way I can fix this without having to send it to a shop. Another thing to add is when the screen goes black the keypad lights up then once the screen shows up again the keypad isnt lit.