Hiya, and welcome to Just Answer!
There are various ways to do what you want, depending on what is actually happening. When you say someone is remotely controlling your computer, does your mouse move around the screen on it's own and you can "see" someone else typing on it?
If you could provide me with more information in regards XXXXX XXXXX you know someone else is controlling your system I can then provide you with the tools you would require.
First thing I would recommend would be to run a spyware scan, if you use a software firewall, turn it up to the maximum setting that still allows you to get out to the internet, (if it's the McAfee or Symantec software firewalls you have) go through and reset the allowed application settings. Then when various programs try to access the internet, it will prompt you and ask if you to approve the access.
If you're at the computer when you see the mouse moving, and actually seems to be controling the pc, open up a command prompt window, and type netstat then press enter, it will give you the ip addresses of all the active connections to your computer. Then you can go to www.arin.net and perform whois queries on the various addresses to try to find out where the connections are coming from. It'll usually provide you with the ISP name, and often contact information related to abuse/hacking coming from those addresses.
Also, if you go into add/remove programs, make sure that all the applications that are listed in there are applications you installed and WANT installed.
One other thing you can do, to find out if there is something on your system, is bring up task manager, then open a google window, query the names of any processes running in there that you don't know what they are, and google should list what the process is, and wether or not it's a malicious process.