Got the HTC connection setup updated lastnight and found the data connection is slightly faster. Maybe for all HTC owner should try that out.

Last time i also got this problem before and i check totally not my computer or phone problem is the cable problem so i tried my Desire HD cable it works so i think your cable got problem.

If not cable problem then your phone might kena attack virus when you enter internet by wifi or 3G.

So try format your phone and reconnect again. ( Remember Hard Reset Not Soft Reset )

Ways to hard reset press the volume button both side and hold it and press the power button and hold the volume button until you saw a instruction screen come out about hard reset one only you release the volume button.