"screen to the old computer does not work anymore" = old computer is hard to steer.
"I want to view the old computer contents from the new computer"
Normally, if the old computer was still working, you could
use File Sharing.
If you can't practically drive the old computer,
you can unplug the hard drive from inside the old computer,
then install and cable it up to the new computer. Alternately,
the old hard drive, can be put in an external USB enclosure,
so it can be unplugged easily when you're done. Using an
enclosure, means not having to open the new computer.
Enclosures come in "USB to IDE" and "USB to SATA". Check the
disk type, before you buy an enclosure.
It's possible to run a computer "headless". Connect the new monitor
to the old computer. Boot into Windows. Set up file sharing. Finally,
switch off the power on the monitor (front button, not the power
adapter), then unplug the monitor from the back of the (now working)
computer. Move the monitor over to the other computer (unplug the
adapter or cord and move it over). Start the new computer, then see
if you can view the shared files or not. I did monitor sharing for
years, before I got a second monitor, so I've "moved that cable around",
a lot.
When it's time to interact with the old computer, you'd then need to
plug in the monitor again.
You can get a monitor from Staples, for around $90. I got some
piece of crap like that (different model number) a couple years
ago from them, it has one bad pixel, but when you need a
spare monitor to run a computer with, it's perfect. No complaints
so far, and it's running right now as a matter of fact. I fully
expected it to blow out after a short time, but it surprised me
by still being in a perfect running state (minus one green pixel).
Acer G205HL 20" LED Monitor
Offer Valid November 9 - 22, 2011!
Available Online and In-Stores. While Quantities Last. Price After Savings: $89.52
http://www.staples.ca/ENG/Catalog/cat_sku.asp?CatIds=&webid=909370&affixedcode=WW
You also have the option, as Seth says, of using VNC. That would transfer
a picture of the desktop to your new computer, and the pixels making
up the image, are updated when they change. It's like "remote viewing".
But you'd still need to potentially play "swap the monitor", until
VNC is running and so on.
(This picture, shows a VNC session in the center of the screen, which is
copying the screen from a remote computer. The user can "steer" the remote
computer via interacting with the VNC window. You use the local mouse
to move the cursor of the remote computer, and the effect updates on
your local screen after a second or two.)
http://upload.wikimedia.org/wikipedia/commons/thumb/7/7f/VNC_in_KDE.png/800px-VNC_in_KDE.png
The cheapest solution is just to move the hard drive, right into the
computer case of the new computer, as that requires no expenditure.
And then, you don't even need to turn on the old computer or think
about it. Buying the spare monitor, on the other hand, will give you
two computers to work with (even if you keep the old one turned off
most of the time). In an emergency, the second, old computer, will
come in handy for making repairs or calling for help via USENET.
Plenty of options, for anywhere from $0 to $90 cost.
Paul