SQL server overrides the CPU and memory distribution of the OS
therefore if you check the task manager it will look like it takes all the CPU and memory.
In case the the DB server is the same as the Application server, maybe you can try to reduce the cpu usage by SQL server using the resource governor, you can find more information about the governor here (<a href="http://download.microsoft.com/download/D/2/0/D20E1C5F-72EA-4505-9F26-FEF9550EFD44/Resource%20Governor%20in%20SQL%20Server%202012.docx">http://download.microsoft.com/download/D/2/0/D20E1C5F-72EA-4505-9F26-FEF9550EFD44/Resource%20Governor%20in%20SQL%20Server%202012.docx</a>[<a href="http://download.microsoft.com/download/D/2/0/D20E1C5F-72EA-4505-9F26-FEF9550EFD44/Resource%20Governor%20in%20SQL%20Server%202012.docx" target="_blank" title="New Window">^</a>])
However if the CPU is 100% due to cpu bottleneck reducing the cpu usage will slow down sql server.
Good luck :)