Well, there's an easy way to tell the difference between the two. If you press Tab ingame when playing on a server and look to the far right numbers, you'll have a ping counter. Lower ping is better. Work out the average of what it is by checking it every 5 seconds or so. Then try lowering the screen resolution and turning AA to off in the graphics options menu. Then do the check test again (make sure you do it on the exact same server)  If this improves it hugely (100+ less from what it was before you turned the settings down, a minor change of 10-15 doesn't count), your PC cannot handle the game online during graphically intense moments (like explosions) If it doesn't, then your problem is that you are trying to connect to servers too far away from you. So then try connecting to servers closer to you (typically the ones at the top of the server browser)