Windows 7: Audio Distortion and Lag

I bought my PC tower back in August 2011, i got it custom made and i use my TV as a monitor now i used to use it with a VGA cable, the computer lagged so bad and also the audio would become static after a while like a robot noise also mouse would jerk across screen it was annoying so i recently switched from VGA to HDMI to see if it would help and it was great after a while but started again. I blamed it on using TV but i've saw that's not the case.
My specs are:
Processor: Intel(R) Celeron(R) CPU E3400 @ 2.60GHz (2 CPUS) ~2.6GHz
Memory: 8.00GB
System: 64 bit Operating system

Should i get a new Tower or is there anyway to fix this?



Thank You