Celestra has the right idea by suggesting a dedicated Halo forum unless your problem is windows related. If you do suspect that it's your pc and not the online servers then we need a little more information like pc/lappie spec and your connection speed.
Also check your Firewall isn't blocking anything as well as any third party apps.
Also if it's merely that the servers are themselves rubbish or no-one on them then maybe try LAN Network mode with this tool running, (requires registering for free account). This is a tool that creates a LAN mode inside a chatroom for many games, handy for when official servers are rubbish or empty.