Hello Alain,
Your problem sounds similar, but I'm guessing that it's a CPU or RAM issue. The visuals in GDT are heavy, and this can cause a "backlog". If that becomes big enough, and there isn't enough CPU power, then Windows looks at GDT and sees that it's backlogged with work and allocates some more CPU time, but not enough, making the problem worse. This results in nastiness like the infamous "Not responding" message, which is best solved by killing the application quite often.
There are a few things you can do to fix this -- all of these revolve around getting more RAM/CPU or making GDT use less RAM/CPU:
- Close unused programs (including ones in the system tray)
- Close and restart Firefox (it gobbles up a lot of memory, but closing and reopening returns memory to your computer)
- Adjust the GDT CPU controls - Reduce the refresh rate (make it a higher number) for the waveforms and the EQ
For this, look in the Preferences (F4) and in the Waveforms and Color Sets window.
I mention #2 there because it's a common program, and can chew up CPU and RAM if you open a lot of tabs. (I sometimes end up with 200+ open at a time. Not the smartest thing in the world to do! 
)
But start with #3. Experiment with the numbers, but make sure to go HIGHER and not LOWER. Higher numbers help with CPU problems. Lower numbers are for very fast computers or computers with a minimal RAM or CPU load on them.
Let me know if that helps out.
As for reinstalling .NET being a pain in the ass, that's an understatement! (Unfortunately it's the only thing that works for some situations.)
Cheers,
Ryan