Is this a problem of my Cable or LCD 40 inch tv?

Hi, I have an lcd 40 inch tv and I use a coax cable to watch tv, and, I must say the picture quality is horendous. Anyway, Lately, Ive noticed this: Whenever theres like a flash in the screen, well, in the middle of the screen, it sorta lags. Like when I see a police siren or some red alert thing, Ill see lag in the middle of the screen. However, I then turned on my DVD, and I put Iron man in it. Well, I saw a scene where there was a red alert thing and no lag. I watched him shoot fire and stuff, but no lag, where as, if it were my cable, I would have definetley scene some lag. O and I play my ps3 with an HDMI, and no lag, well, not in the middle of the screen anyway. So is this lag my cable's fault or my TV. And if its the cable, which seems that way, well, can it eventually screw up the screen with the lag? thanks!