why does my computer periodically keep blocking out my internet
connection to my desk top pc.i have a wireless modem with a lap top
sharing the same connection and the internet connection is fine
through the lap top but the connection seems to stick after so long to
my desk top. i have to unplug the power supply to the desk top in
order to shut it down and when i start the desktop back up the
internet connection is fine
again.For somme reason every now and then after about half an hour of
working fine it blocks out the internet and "freezes". any suggestions
or advice on what to do please.

Can you be more specific about what kind of computer you have, where
you got it, and what operating system it is?

You may have a hardware or software problem that is causing your
computer to freeze.  Such problems are very hard to diagnose, and one
usually has to systematically start eliminating possible causes to
determine what is actually going on.  It is often not cost-effective.

do you have torrents running because that could saturate and
overwhemled your router/modem?

Is someone using a wireless phone when this happens?