I had the issue that the DB2 control center did no longer start. You just saw a command windows and the splash screen appearing and both disappeared after a few seconds. The solution was to cleanup some files.
On Windows go to "c:\documents and settings\allusers\application data\ibm\db2\db2copy1\db2". Now delete the following files:
Go also to the "c:\documents and settings\allusers\application data\ibm\db2\db2copy1\db2\tmp" directory and delete the temporary files which are there. Afterwards you DB2 control center should start again.