There are fixlets on BES Support to restart the client service; of course, if the server won’t receive a good report from the client for days, the restart action will expire.
If some of your clients are not reporting, you should investigate the issue (firewall/proxy misconfiguration, corrupted reports, connection issues, performance issues on FillDB, etc.).
If your clients are crashing for some reason, for Windows systems the BES Client Helper is available. Even in this case, an investigation about the reason of the crash is recommended.