This is normally quite a simple problem to fix by a TV shop or a confident (and sensible) user
<b>!!Warning!! when working on the inside of a monitor be carful even with the power turned off!!</b>
1. Unplug the monitor from the mains and PC.
2. Remove the back cover.
3. Locate the HT tranformer (this is normally a covered in black plastic and 4"x4"x6").
4. on the HT tranformer you will see 2 POTS (look like plastic screw heads) one is for adjusting the Focus the other for the Brightness.
5. Plug the monitor into the mains and the PC and adjust the focus by using a phillips head screw driver to turn the POTS and whtching the screen (or having your friend to watch the screen).
6. When the screen is in focus disconnect the power and signal cables and replace the cover.
7.Power on and check it's still in focus.
If the monitor starts to drift out of focus again then it probably has other more serious problems and will need a visit to the shop or replacement.
P.S. be carfull what you touch the HT leads can carry 25-30k Volts on a 17" CRT.
Only the insane prosper.
Only those who prosper can judge what is sane.