Game is great, but a few minutes of playing, I can't use the mouse. It goes to the left side of the window and stays there. No matter how much I move it to the right, it doesn't move.
And after this I lose the game because the only way to exit is pressing alt-ctrl-del and killing the exe.......
Has anyone else found a solution to this?

Try looking here -
http://www.gog.com/forum/theme_hospital/does_anyone_else_keep_having_their_cursor_stick_to_the_top_of_the_screen
or here - http://www.gog.com/forum/theme_hospital/mouse_problems

Don't move to the right, move to the same direction it have stuck. E.G: Mouse stuck at left? Move HARDER to the left, shortly the mouse will unlock and you will be able to move around the screen. To avoid it blocking again, move around the scenario with keyboard arrows. Or just save and quit the game.

Either way, you can press ALT + S to quick save the game, then quit without worrying about losing your progress.

This is a common problem in Theme Hospital. You can see previous posts and [url=http://www.gog.com/forum/theme_hospital/mouse_problems/post19]here.

First thing you want to try is unchecking "enhance pointer precision" in the mouse settings.
If this doesn't help you with your mouse, well, there is nothing more to do than restart the game. If you don't want to lose your progress in the current level you should quick-save your game or try to unstuck your mouse as montcer9012 suggested. (This is what actually worked for me!)
Don't worry about it. This is a minor bug this game is known to have. Other than this (and a couple [url=http://www.gog.com/forum/theme_hospital/disappearing_doors]bugs) it's a GREAT game and I enjoy it every time!

I found that even in the recommended compatibility mode - Windows XP (Service Pack 2) - unchecking 'enhance pointer precision' in mouse settings didn't work to resolve the problem reported in the original post.

As a consequence, I'm trying something different and so far, it's working:

In the Compatibility mode selector are some Settings options. I've selected to 'Run in 640 x 480 screen resolution' and to 'Disable visual themes'.

I'll report back if this apparent sucess changes and my mouse pointer decides to abscond to the left.

N.B. Well, I managed to play for around 5-6 hours before my mouse went to the left, but it did this only after I'd been zipping it around the screen to check my 3 buildings. I've a feeling this may have been a factor.