Hi Mark,
I agree with Tim's suggestion to install latest Management Pack Update first.
At the same time, please also check KB939799:
The System Center Operations Manager 2007 agent is unable to restart the health service after its monitored thresholds are exceeded
http://support.microsoft.com/kb/939799/en-us
If the issue persists after installing the latest SCE patches, please let us know some more detailed information, such as when and where did this issue occur? Is there any special changes (for example, adding software/hardware) performed recently on the SCE computer (which may also cause this problem)?
Thank you for your time.
Sincerely,
Robbin Meng
Microsoft Online Community Support