all my games on steam lag but my internet for web browsing is fine

i have been having this problem for about 3 weeks now. my computer is a alien ware so i can play any game fine. but when i go on steam i get mouse lag, and when i enter games i get the mouse lag again. When i enter server's it goes to my normal ping,in about 5 seconds it jumps 200-400 ping then goes right back down to normal for 1 second then right back up to high ping again. my game doesn't freeze when this happens but it will lag me shots. so i thought i was my internet but when i go web browsing it loads fast all the time, no mouse lag and it never freezes. i clean my pc,i turn her off, I got spy bot Search & Destroy and Microsoft security essentials. i use google chrome for the internet and i get no pop ups. so i really don't know what is going on with steam. so if anyone has any idea on what to do or what might work please help me out. thanks

via Bleeping Computer Last 20 Posts http://www.bleepingcomputer.com/forums/t/512643/all-my-games-on-steam-lag-but-my-internet-for-web-browsing-is-fine/