Installation of CES
My local got several sitecore instances running with one Coveo server. For some reason, after restarting machine, the CES turned off. Even manually turned it on, its dead again. I have tried to uninstall it and install again, same issue occurred. Any suggestion would be much appreciated.
Using a single CES server to index a lot of Sitecore instances is not recommenced by Coveo unless you have very powerful hardware and tweak the CES caches sizes for performance.
Since each Sitecore instance creates multiple sources, fields sets and other type of configuration objects in CES, one of the cache to increase in size if the CES configuration cache (see The ConfigObjectCache is swapping to disk. Performance might be adversely affected in CES Admin Tools).
This might not be your issue. As @mlaporte said, first check the Windows event logs and also the CES index system logs. If that doesn't help, I recommend you to open a support ticket as this kind of problem is not easy to troubleshoot on a Q&A website like this one.