To resolve the Compositor issue, could you please close out steam, and reopen as administrator? If that does not work to start the compositor, you may need to uninstall and reinstall Steam.
Regarding the issue with the HMD; If you get the compositor working it may clear up the issue you're having with the HMD. If it does not, please try the following:
1. bypass the link box and connect the 3in1 cable from the HMD directly to the PC and test it.
--If that doesn't help--
2. try to bypass the link box and use the short HDMI and USB cable and connect it directly to the HMD.
Plese let us know the outcome of these tests.