To my knowledge, the Windows built-in defragger is a Lite version of Diskeeper and is NOT capable of being set for scheduled defrags.
You would require the full version of Diskeeper or some other third party software to have the capability of setting scheduled defrags.
It doesn't hurt to defrag every once in a while but frequent defrags are not required on NTFS volumes as the smaller cluster sizes already reduce fragmentation. The defrag software manufacturers will throw impressive numbers at you but in actuality the performance gains are minimal unless you are dealing with large file such as those encountered from ripped movies.
What Operating System?
What file system?
Right click on the taskbar and select Task Manager..., choose the Processes tab and take a look at the running processes. Most people's system have a ton of unnecessary processes running that saps the resources. Typically on my system, Windows 2000 has about 23 processes runnung and Windows XP about 26 processes.
Compare all running processes with the list from Pacman's Startup Application List.
Here are the keys for the list.............
"Y" - Normally leave to run at start-up
"N" - Not required - typically infrequently used tasks that can be started manually if necessary
"U" - User's choice - depends whether a user deems it necessary
"X" - Definitely not required - typically viruses, spyware, adware and "resource hogs"
"?" - Unknown
Terminate unnecessary, rouge and unknown processes using msconfig.
Run malware detection programs such as Ewido, Ad-aware and Spybot Search & Destroy to see if you have spyware or malware on your system. Make sure that you update these programs after installation to increase effectiveness.
It's a good idea to clear cookies and Temporary Internet Files before doing malware scans or they my be detected as false positives.