yahoo reply is not functioning

Sir,
1) In only one system in my network, replying from the yahoo site is not functioning. The same case is for yahoo messenger. But the same yahoo mailid is working fine in other systems.
2) Another case is, rediff.com site is very slow in one system. Comparatively, it is fast in other system while checking the rediff mails.
Can i have the reason and the solution for the above cases.
Thanks & regards,
P. Sampath kumaran