I have all of a sudden started to get a popup message on the taskbar
that "Network cable is unplugged", and thus unable to use internet.
This message appears repeatedly, i.e., pops up, disappears momentarily,
and again pops up, and this goes on. My PC (Windows XP Pro) is
connected to the internet though my Institute network LAN.
I think I didn't install or run any new program which might have caused
this problem, since I used the internet successfully before leaving for
home in the evening, and next morning the first thing I found, at
switching on the PC, this problem.
I have tried re-inserting the cable many times, but no success. On
inserting the cable, the green LED on the card goes ON.
The probability of some hub or switch being switched off on the other
end is also low, since internet is working properly in adjoining
rooms.When I Ping, it says "destination host unreachable".

Any tips would be appreciated. Is there a way to check if my LAN card
or cable are alright (preferably without replacing them)?