CPU constantly hitting 100%

Hi Experts,

we are facing CPU 100% usage, it is constantly hitting 100%.

what I did was:

checked for any blocking, no blocking session found.

identified the long running query, user killed it as it was creating lot of issues.

Now,

The server with which issue is having 7 instances with 72 GB RAM.

SQL Version is Microsoft SQL Server 2008 (SP3) - 10.0.5770.0 (Intel X86)   Dec 29 2011 14:25:37   Copyright (c) 1988-2008 Microsoft Corporation  Enterprise Edition on Windows NT 6.1 <X64> (Build 7601: Service Pack 1) (WOW64) (VM).

I have googled, found the answers what I did, but not for many instances on single server.

how to figure out which one(OUT OF 7 INSTANCES) is using up all CPU.

Please help me.

Thanks in advance.