Here is how to create an unattended disk cleanup which will also
empty your prefetch folder .

Create a new text file and place the following contents inside
just copy and paste the below lines in notepad.

c:\windows\system32\cleanmgr.exe /dc /sageset: 1
c:
cd \
cd c:\windows\prefetch
del *.* /q
Save the file, with the extension .bat
Suppose name it diskclean.bat

Double click the file. This will run the Disk Cleanup program in a
specialmode which asks what items you want cleaned when Disk Cleanup
performs an unattended cleanup. Check the items you wish to be cleaned
up, then click OK.Now again Right-click on the diskclean.bat file and
click edit. Change the first line

c:\windows\system32\cleanmgr.exe /dc /sageset: 1
to
c:\windows\system32\cleanmgr.exe /dc /sagerun: 1


Save the file.

You can execute this file in place of running Disk Cleanup, or
, to have this program run unattended, run the Add Scheduled Task
Wizard in the Control Panel and create a scheduled task using
the diskclean.bat file you just created.

Enjoy!!!!