CS:S Problem

[Zemfik]

I've been playing CS:S for a few weeks now no problem. I have recently been getting on and it has been unusually laggy. I have no idea what the problem is. I can see my grenades going but you'll see it in stages, hard to explain. Everyone that is running you see like every 4 steps but not the movement in between. It's really pissing me off and I can't figure out what's wrong. I tried uninstallating and reinstalling with no luck. I'm not sure if this is a hardware problem or not... Any ideas? It might also be my router...