SQL Server, by default after an install, will attempt to use every bit of CPU and RAM that the system will let it have. Assuming you've changed none of the default settings, this is the amount of CPU & RAM that it currently needs to satisfy the query. Although, on the RAM side, you also have to take into account, what else is running on the system, because other things, from the OS to other programs, could be using up RAM, so SQL Server can't allocate more.
Check that you haven't set limits on the CPU through the affinity settings. Check that you don't have a limit on RAM that is too low (you should have a limit, but it should allow for enough memory for the OS, say 2gb of the top, so SQL Server will be limited to 14gb). The fact is, you can only limit the amount of RAM or CPU that SQL Server uses. You can't make it use more.