I bought a Compaq desktop computer as a wedding gift for a friend in
the UK and shipped it to him. He bought the necessary electrical
adapter and changed to the proper voltage he can't get the monitor to
work. it will not work with any monitor. It boots up but no matter
what monitor is attached nothing can be seen. Do you have any idea
what could be wrong?

I would take off the cover and press down all the cards, etc.

It's possible that something has worked loose in transit.

Of course, switch off the power before tickling around inside.

A further thought ...

If that doesn't work, why not give Hewlett-Packard in the UK a call?

They now own Compaq and the kit you bought probably came with an
International Warranty.

I've used the H-P Help Line for various probs with Compaq & H-P kit
and they're always most helpful. At a pinch, they may want the stuff
to be taken to a local dealer.

personally I'd get the computer sent back, return it and buy an
american computer since they are much cheaper over there. However HP
do offer international warrenties and have an excellent customer
service. I would make them the first port of call.

American computers work fine with European power adapters. It is
likely that the computer was damaged during shipping somehow.

Ask your friend to try replacing his video card. If he doesn't know
how to do this, most computer repair shops can step him through the
process - for a fee, of course - or perhaps he knows someone
tech-savvy around him. If the problem is not simply with the video
card, there may be more significant damage to another component. This
is likely more of a case for your friend's local technicians than
Internet advice.

95% of problem with dispaly on the monitor are due to Memory module
sitting on the motherboard of your computer and 95% of the times the
issue is resolved by removing the memory from the computer keeping it
our for 10min and putting it back firmly in the slot. I am sure this
will resolve the issue. Try it and let me know