If i'm supposed to give U a suggestion than i would say this ....
read my lips :
" Get some MODEM from ne of ur frd which U know is working ..& try it again ... if problem persists then reinstall IE6 ..still problem persists then reinstall Windows ....i'm sure with ur configuration it wont take more than 25 minutes to reinstall it with complete formatting ..so just have patience ." I really believe it's the problem with ur MODEM ..u wanna know the reason ... Man!! i have suffered from the same problem for ard 10 days ...
& when i just for a trial replaced my MODEM with a new one it brought wonders ... i was very happy !! bcz my yahoo! mail was signed in front of me .... & eventually on my new troubling dabba ( it's a nickname for system unit

) ...
enjoy