Device Manager should not be freezing, that is indication of a bigger probem. In the meantime...
What kind of registry repair scan are you using ? I use CCleaner.
If your hard drive does not have much free space available, you will have all kinds of problems, try copying all unimportant data off to CDs or DVDs or an external hard drive.
If you are not using hibernation, that has a large file reserved for it on the hard drive, turning off hibernation frees up the space.
System Restore takes up a lot of space, if you have it turned on. You might try a restore to a week or two earlier to see if your computer begins working fast again. Or you can turn it off and thus free up a lot of hard drive space, but you lose the ability to "roll back" your computer to an earlier date.
You can install a bigger hard drive.
It is possible your paging file is badly fragmented, and the Windows defragmenting program does not touch that file.
If you are using Windows XP you can use a program from Microsoft to defrag the paging file:
http://technet.microsoft.com/en-us/sysinternals/bb897426.aspx
This program does not work with Vista.
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There is a way to remove the paging file, but some programs don't like it when that file is missing. I've had no problems.
The trick is to tell Windows you want no paging file. Then you reboot to make the computer start with no paging file present, then run Disk Defragmenter to gather your files together to get a big chunk of free space together, then reboot, then tell Windows you want the paging file, and reboot the computer again to make it so. Here's how to do it with Windows XP:
Control Panel
System
Advanced tab
Performance Settings button
Advanced tab
Virtual memory - Change button
Click the "No Paging File" button
Click OK
shutdown the computer and reboot
Try to run Disk Defragmenter
When that is finished, shut down and reboot
Control Panel
System
Advanced tab
Performance Settings button
Advanced tab
Virtual memory - Change button
Click the "System managed size" button
Click OK
shutdown the computer and reboot
Now see if the computer runs faster.
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