My screen sometimes has a dead spot on it. It is quite difficult to explain
but when it occurs there is a square in the middle of the screen about 10cm X
10cm where nothing works. You can still see every thing on the screen but you
can not click it within this square and when you try it deselects what ever
is currently on the screen. Outside this invisible square you can click and
control the page as normal.

It can be solved if i end the program dwm.exe in program manager. the
program starts again after it has been ended however the problem of the dead
spot is fixed.

any explanation and/or solution would be much appreciated

I wish I had a solution, but I've seen it, too, unfortunately. I've talked
myself hoarse over how flaky the new shell is, but honestly, I rarely see UI
bugs fixed in Windows, so I expect it to only go away when MS replaces the
shell. Other flaky things that may be related: have had a window go
permanently on top of the desktop (not an app that supports setting its own
z-order like that), dragging files with the preview showing files dragged
(and deleted) hours before, deleted files still showing up on the desktop
even though the file is gone, the digital clock on the system tray ceasing
to update without resizing the taskbar, VPN connection system tray icon
sometimes shows a connection that's there...sometimes it acts like you
disconnected when you aren't. I've run into probably twice that number, and
most are pretty in-your-face (my favorite so far in that it's caused
problems in web development for me is how Vista will not install ASP.Net
from the new Windows Features "tool"....won't give you the reason, but
spends 15 minutes before failing. the solution involves doing into some
system files and removing them.
Could be something about the desktop's refreshing being horribly broken
(good reason to port this thing over to WPF), so you *may* have some luck
clicking on the desktop (to give it focus) and then hitting F5 to force it
to redraw itself.