here's my problem:
Usually, I play CS, TF2, BF2142 etc. my ping was 30~40 in a server. But since this week, it goes up to 140+ constantly untill past 12:00am. In this case, I can't play at all.
I've never installed any software since last month, and I tried other computers, they all have the same problem. Also, I tried connecting w/ my friend's internet( from another ISP), then my ping goes normal. My ISP told me that my internet connection is fine, but I can't find any other solutions to this.

Please help!!!!!

BTW, I got BitDefender and SpySweeper. So it shouln't be virus....

My guess will be someone else in your network is downloading and if that is not the case you should contact your internet service provider and let them do some test with your line.

Also check on speedtest if your internet speed is normal. Or that it is extremely slow.

the game server can be overloaded with too many players.

monitor the time of day when all is well and then when it is poorly --
evening times will always be stressed.

well, speedtest shows that my download is more than 5500kb/s, upload is about 700kb/s, and latency is around 40ms to Chicago, which is pretty normal for me.
But once I tried to connect to CS, TF2 or other servers, my ping is higher than 100...
I'll try re-install my games today

you've missed the point; your ISP rates are good, but the game servers are poor.
you should reach the conclusion that it's related to the game server.

I asked one of the game server provider, here's their reply:

"This problem appears to be caused by your ISP overloading one of its peering connections. The issue occurs at their border router on the outbound to you as well"

"Unfortunately InterNAP told me they can't route around this. You'll have to ask your ISP to fix their connection to their upstream"

I'm so confused.........

the point is that your system is just fine and you are at the mercy of the ISP and everything beyond it.

Thanks. I think the ISP has already fixed it after I wrote them a email. =D