Explorer Very Slow and Nonreactive

1. Download Sysinternals' Process Explorer
2. Run the program with administrator rights (so it can access all the information it requires from the system).
3. Right click on the process Explorer.exe, and select Properties.
4. Select the performance tab.
5. Now open a new Explorer window, and watch the graphs. You should be able to tell whether the problem is i/o access or cpu (I haven't found the memory to be a probable cause for this behavior).
6. Other tabs like Performance and Threads, should help you to figure out what's abusing the system's resources.

If you reckon the problem could be some corrupt dll or handler attached to the Explorer process, then follow these steps:

1. Download Sysinternals’ Autoruns (it doesn’t need to be installed).
2. Uncompress the zip file and run the program autoruns.exe with administrator privileges.
3. Wait for the program to retrieve all the information, then select the Explorer tab.
4. Look for any item without a publisher or from a dubious source.
5. If you find any, disable the item by un-checking the box to the left, then close the application and reboot the system.
6. Repeat the process with any other dll/handler you think it could be causing the problem. Reboot again after each one (you can also re-enable the items by checking the corresponding box).

Hope that helps.

A checklist,

• Do you have network mapped drives? that may be causing stalls
• Do you have fragmentation on the primary drive? that makes enumeration in explorer slow
  • try JkDefrag -- Do not trust the built-in defragmentation support
• Do you have page-file fragmentation, that makes a lot of things slow
  • try PageDefrag -- if you start this app, it will tell you which system files are fragmented immediately. You can then choose to defrag with a reboot
• Windows support note on other application conflicts
• Confirm that this Windows machine is at the same service-patch level as the other systems that do not show such problems
• Consider turning off Indexing Service -- this is not exactly known to cause such slow-downs, its supposed to work only in idle conditions, but its a waste anyways
• Is your Windows configured to show ZIP files as folders?
  • This is known to cause problems
  • would suggest shifting to 7-zip anyways.

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Some more things you can try.

• The autoruns check is a good idea,
  did you find any new or unexpected start up activities engaged there?
• Did you make any recent driver or system updates?
• There is also a possibility of system file corruption. You can check for that
  from the Start, Run with a "sfc /scannow" or "sfc /verifyonly" command.
  It will take some time to verify all Windows files are intact

I would try Process Monitor from Sysinternals which should allow you to see what sort of file accesses are being performed when you open a file.

As I understand it, Explorer attempts to find icons for each file which sometimes attempts to locate the associated application, (so it shows the excel icon beside a excel file etc). However if there is a application located on a network folder (or on a memory stick) then this can slow it down. And of course if the drive path is not there, eg a memory stick that isn't plugged in or network path it can't find, or if permission to the file is denied, this will slow things down.

Process Monitor will also show you lots of other stuff that goes on when you open a windows, for example, sometimes when explorer attempts to access an application to determine the file icon, this triggers an anti-virus scan.

Note the icons were supposed to be cached, to avoid repeated look ups, but that may not be happening. There is a registry key which controls the size of the cache

Hkey_Local_Machine\Software\Microsoft\Windows\CurrentVersion\Explorer\Max Cached Icons

(Mine is set to 2000, but maybe you can try increasing it).

The cache can also get corrupt, but I never heard of this causing a slowdown, rather it sometimes causes the icons not to be drawn correctly.