PC go website very slow

HI, I am using i-cable.

I am using TPlink N841 router with cable connection.

1. my PC using Cable , if I ping hk.yahoo.com, speed is ok 11ms or 12ms.

But if I use FIrefox,IE go to hk.yahoo.com the speed is very slow to show all screen.
And if I go to HKEPC.com/ youtube.com, all need to wait a while to load, BUt last week is very fast...

2. I have iphone/pc 2 using wifi for same router, but if I go to same website, seem the speed is better than my PC.

I suspect something wrong in my PC (XP) ? so affected the browser?    I did test 2 Lan card/ Lan cable or not use Router too......
did check spyware/virus etc, and unisntall some unuse software but same.