Help needed urgently, steering jerking to the left when driving??

Hey guys ive been having a problem with my Da and was wondering if anyone could tell me what the problem is??

I parked my car, which is very low in 6" of snow a few weeks ago for about 4 hrs when visiting my cousins, on my way home it developed a very hard jerking in the steering generating from the front left, its an intermittent tug on the steering which gets worse the faster ya go and only happens when under driving, doesnt happen when coasting or decelerating, i had someone look at it and they reckoned track rod end which i replaced this evening and its still happening?? i was thinking it must be something to do with the shaft but also maybe the wheel needs balancing as some of the weights may have come off???

Has anyone had this problem or can anyone tell me wtf is wrong, getting sick of having to drive my girlfriends car!

Cheers for looking

Tommy