I recently bought a Nvidia GeForce 6200 256Mb AGP

Sounds like a Driver Conflict.
Still have the old 5200 drivers in there?

Did you install the drivers for the 6200, BEFORE you physically put the graphics card in? (Not shouting)

Let's say you did remove the 5200 drivers, before you installed the 6200 graphics card.

BUT,
If you physically install the 6200 graphics card, BEFORE you have installed the drivers, Windows 'sees' a new device, and hurries up to match one of it's generic drivers.
(Windows has thousands of drivers!)

Now you come along, and install THE drivers for the 6200. Windows has a drivers conflict.
Windows: "Which drivers do I use? These, or THESE?"

Makes for a garbled graphics display as you've described.

If the above is true, start over.
Go to Add/Remove Programs, and Remove the Nvidia software. All of it that has Nvidia next to it.
(THIS, is provided of course, that the computer HAS Integrated Graphics, and does not just use a graphics card. You will be plugging the monitor, into the VGA port in the I/O area, on the back of the computer temporarily, if this is true, and this computer has Integrated Graphics)

(Start>Control Panel>Add/Remove Programs) If there is more than one Nvidia program listed, Do No restart the computer each time you remove one. Do Not restart. Read on)

After all Nvidia software has been removed, close Add/Remove Programs, close Control Panel, and return to the desktop screen.
Shut the computer down normally. (Start>Turn Off Computer>Shut Down)

Unplug the computer from power.
Press the Power On button in, and hold it in. Hold it in for a count of 5 seconds. (Count, 1001,..1002,..1003,..1004,..1005) Let go of the Power On button. Do this procedure Two more times.

What you are doing is clearing any CMOS Error Codes, and resetting BIOS back to the factory default settings.

Open the case. TOUCH the metal frame of the case to relieve your body of Static electricity. Remove the 6200 card. Plug the monitor into the back of the computer into the VGA port. Leave the case open, you'll be going back in there.

Plug the computer into power. WAIT 1 minute, then turn it on. After Windows has fully loaded, install the GeForce 6200 drivers from that CD disk. Do Not restart.
Shut down normally.

Unplug from power. Touch that metal frame again. Install the GeForce 6200 card. Close the case. Plug the monitor into the GeForce 6200. (You did plug the monitor into the 6200 the first time, right, and not the VGA port?)

Plug the computer back into power. WAIT 1 minute. Turn the computer on. Go to Start>Nvidia>Nvidia control panel, and set the settings.

It could easally be the fax is sticking or broken - check this before anything else as when the graphics chip on the card is under a heavy load it will heat up quite a bit. Hope this helps. Replacment fans can be purchased on ebay of if the card is under warrantee you could send it back