Did you make any changes to the computer recently?
Boot into safe mode and check if your system freezes again.
Steps to boot to Safe mode
1. Restart your computer if it is powered on.
2. Tap the F8 key after your computer initially powers on.
3. Once you see the Advanced Boot Options menu you can stop tapping.
4. Use the up/down arrow keys to highlight your selection.
5. Select Safe Mode and press Enter.
6. You should see drivers loading, and then Please wait.
7. You should then be at the Welcome Screen.
8. Logon to your computer using an account with Administrator privileges.
Start your computer in safe mode:
http://windows.microsoft.com/en-US/windows7/Start-your-computer-in-safe-mode
If you do not get the same problem when booting in Safe Mode you can go ahead and do a Clean Boot in normal start up. There might be some background program that might be conflicting with the Explorer.
A clean boot helps eliminate software conflicts.
To put the system in Clean Boot:
1. Log on to the computer by using an account that has administrator rights
2. Click Start, type msconfig.exe in the Start Search box, and then press ENTER to start the System Configuration Utility.
If you are prompted for an administrator password or for confirmation, type your password, or click
Continue
3. On the General tab, click Selective Startup, and then click to clear the Load startup items check box. (The Use Original Boot.ini check box is unavailable.)
4. On the
Services tab, click to select the
Hide all Microsoft services check box, and then click
Disable all
Note Following this step lets Microsoft services continue to run. These services include Networking, Plug and Play, Event Logging, Error Reporting,
and other services. If you disable these services, you may permanently delete all restore points. Do not do this if you want to use the System Restore
utility together with existing restore points
For further information on clean boot please follow the below given link:
How to troubleshoot a problem by performing a clean boot in Windows Vista or in Windows 7:
http://support.microsoft.com/kb/929135
After you have finished troubleshooting, follow these steps to start the computer in normal mode.
1. Click
Start, type
msconfig.exe in the
Start Search box, and then press ENTER.
If you are prompted for an administrator password or for confirmation, type your password, or click
Continue.
2. On the
General tab, click the
Normal Startup option, and then click
OK.
3. When you are prompted to restart the computer, click
Restart
Hope this helps!
