Ok guys, I require an urgent help here.

I am trying to debug this issue:

I have Windows XP loaded on my PC. I applied for the MTNL broadband connection. But when I tried to connect using this external modum that was provided to me by the service provider (MTNL) the interconnect could not get connected. The connection kept getting connected and disconnected for each few seconds.

Then..
I suspected that may be its an issue with the operating system. So I loaded Windows XP again. But the issue could not be resolved.

Then...
I assumed that the PC's LAN card is faulty. So I replaced it. Loaded the new driver and was expecting the issue to disappear completely.

I am trying it again...but the connecting is not working. Whenever I try to connect the internet the connection keeps getting connected and disconnected.
Can you help me debug this issue?

What should I check?