Your Mobo is socket 939, which is too old to realistically upgrade the processor. You mobo also uses standard DDR400, which is also outdated. With that in mind I think its time to think about a new computer!
Please can people advise me. Also I want to be able to play videos from the PC on my TV but not sure how. can this be done wireless?
See here: http://www.whdi.org/
Best of luck.