These are probably two of the most frequently asked questions in the Technet SCVMM forum.
The first thing I'd ask people to do is to check the FAQ published on Connect site along with the beta bits, which covers the known issues and limitation for this beta release. One of the things we documented there is that a USB drive could cause your host be in this "Needs Attention" state. We're fixing the issue for our RTM release.
Secondly, I'd recommend you to check the troubleshooting note published for our VMM 2007 release, which covers a lot of commonly seen and known issues for both add host (or agent install) scenarios and hosts in "Needs Attention" state. The most commonly seen causes of failure are:
Lastly, here are some additional testing you could do on your host to unveil issues with services that VMM is dependent of:
If above resources cannot help you find the root cause, try collect debugging traces by following the instructions posted here, study the trace logs and look for exceptions from the traces to get a clue on where things might have gone wrong.
Hope this helps and thanks for reading,