UA-25EX Stops running in Windows 7

I am having a problem with the UA-25EX in Windows 7.
I've installed the Windows 7 driver. It has operated OK until quite recently when I started to notice that it stopped operating. This has happened while listening to music files, viewing Youtube vids, whiel operating music editing software.
The result is no sound. Sonar X1 tells me that there is no sound source for output. Other software tells me that the files I am using are not recognisable and therefore cannot be played. THis includes wav files.
THe only solution I have is to reboot and then everything runs fine until the next time it decides to glitch.
Any suiggestions?