In VPS server if i start IIS7 then error is coming like this cannot start service w3svc on computer '.'. what is the solution for this?
TOTALLY IRRELEVANT. Seriously. This is a Windows install of whatever sort, and whether this is physical or virtual hardware is as relevant than what you ate for breakfast.
Get a professional admin looking at it ;)
Anyhow, get the error message. What you post here is NOT the error message by IIS, it is basically a generic error message by the service manager.
Consider - just in case you want to get this solved - to look into the event log and hunt for a real error message. A starting service can not provide any sensible information (the service manager API is not having a concept of this), and anyhow the windows accepted way to do that is to write one or more events into the event log. I am sure you will find some warnings or errors there.