Bluetooth Problem

The sound on my Bluetooth headset cuts out after literally 2 or 3 secs.ng.

Dell desktop with a Belkin USB Bluetooth Adapter (Widcomm Driver
4.0.1.2401) paired with a Plantronics Voyager 510 Headset (and a Motorola
phone)

I am assuming it is not a hardware problem as:
1) The headset works fine with the phone.
2) I can transfer files (photos) from the PC to phone OK.

But when I play music or speech (Skype) from PC to headset it plays for
about 3 secs then cuts out. If I switch headset off and on again I get
another 3 secs.

Any suggestions?