HTC Desire HD — Bluetooth turns off automatically

Since a few days I've got the following problem on my HTC Desire HD.
When I'm activating Bluetooth it starts up quite normally, but after a few seconds the bluetooth connection turns off automatically.

No (whatever) restart, no taking out the battery, sim card and so on helps.
Has anybody got an idea (or encountered the same problem) to solve this behaviour?
Thanks in advance
Robert

Bluetooth finally works again and for all who've got similar problems:
- Changing the antenne (integrated in the cover of the accu slot) didn't work
- Deleting all bluetooth apps (or apps that use bluetooth) didn't work either
- Reloading the rom didn't work, too

Only a complete handy reset and reinstall "brought bluetooth alive" again.
(all apps, data and so on naturally were lost - via play store at least the apps were restored rather quickly)
Robert