I made a fresh XP installation on an empty and formated partition today.
SP3 and all MS updates installed.
System, audio, video etc. drivers are installed,
then Firefox, Safari, Crome and WAMP,
that's it, nothing more.
I installed FB4 beta and it ran fine!
Test projects behaved as expected etc.
I closed FB4 a few times and opened again . . . everything great.
I restarted the machine and all was still fine.
Until now I always had the "Trial / Serial Number Dialog" pop up and chose the trial.
Then I entered the serial number I received from Adobe and FB4 Beta stoped loading . . .
just the Flash Screen . . . "Loading Project" progress and . . . exit, no FB4!
Adobe Team, please help
Kaushik Mukherjee provided a workaround in his reply here:
So . . . I uninstalled Flash Builder,
installed the Eclipse Plugin Version using bundeled Eclipse.
Installed Flash Builder 4 Beta.
Only after creating one new Flex Project in Eclipse, the Flash Builder started up again using the serial number I entered before.
Not a very elegant workaround, but it fixes the problem.
I filed a bug report, but the Adobe Bug System indicated that I created a bug that I have no permission to watch so I cannot enter the found workaround.