How can I tell if someone has put a keylogger on my pc,and how can i prevent it from working?

Answer 1

It is possible that a rootkit has been installed on your system in which case no antivirus or spyware will detect it. Rootkits can hide files and running processes rendering them virtually undetectable. There are several good (and free) rootkit detectors that you may want to try:

http://sectools.org/rootkit-detectors.html

Answer 2

The only way to detect a hardware keylogger is to find the device itself.

Software keyloggers however, are generally detected by one of the following:

Spybot search and Destroy

Adaware.

Download and install them both. Update their definition files and run a full scan of your system. (Use one program at a time, not both at once)

Also activate Spybot's "Teatimer" function.

Answer 3

You could use a programme like Ad Aware to run a system scan and tell you if there is anything like that.
You can also look in the Windows Task Manager to see what items are currently running, although a key logger will often show under a false name.

Answer 4

Adaware (free) or Spybot (free)

Will Both find and remove most software Keyloggers.

Web search will find them both for download