This is a well known version 1.7.4 issue that seems to emanate from Win7 64 bit using the installer version.
The remedy at present seems to be uninstall the installer version and download the archive zip version then run the setup_xampp.bat file.
The above from the German language forum:
viewtopic.php?f=4&t=44260BTW steini has moderator privileges on these forums.
Also I noticed an old German language reply (2007) that mentions ZoneAlarm as perhaps having some influence on this issue - temporarily disable, restart your PC and see if it still occurs, if no difference then enable ZA again.
In older versions this issue sometimes occurred if XAMPP was installed to a path with a space in the name or even not in the root of a drive or partition in a folder not xampp for example it should be in C:\ D:\ etc. in a folder named xampp.