BSNL Wired Login problem with laptop but desk top is working

BSNL wired Broad Band connection. With same userid and password, using desktop I am able to connect to the net. But using laptop and same userid and password is not working. It used to work before with laptop also.
1st time I got a pop up window with redial timer, I clicked cancel and later I tried to connect again by clicking the connect icon. Then the login page came up as usual, with out me doing any thing the cursor went into the userid slot. By the time I clicked connect it wiped out the userid. Since then I could not connect using laptop. But the same userid is working with desktop.
I tried flushing DNS, resetting the modem. Unplugging the wires. Scanned with anti virus. It is giving 691 error code. But the same userid and password is working with desktop.
Any advise please.