Some users are finding that the registry search feature hangs at a certain point. This problem does not manifest on a clean system without any third party software installed. Possible causes are outlined below.

The search does not hang, but is only slowed down
Make sure that you wait for long enough. A registry filter, a lock or something else may be slowing down the search operation. Leave it running for at least several minutes and carefully check the Results section on the left of the screen to look for updates.

Possibly there is an aggressive security product installed which blocks the search operation
An aggressive antivirus, anti spyware, firewall or other security product has a registry filter installed which blocks the search operation. The product may have a "don't touch my keys" policy to prevent tampering. This measure is often to prevent viruses or other malware from attacking the product. Try removing or disabling the product to see if it resolves the issue. If it appears that searching with Regedit does not exhibit this problem it may be because the product includes an exception for that tool. Checking at what registry key the search process actually stops may help you find the product causing the problem.

Possibly there is an another type of product installed which blocks the search operation
Instead of an anti malware program, there is another program installed which finds it necessary to block access to its registry keys, possibly as an anti-piracy measure. If it appears that searching with Regedit does not exhibit this problem it may be because the product includes an exception for that tool. Checking at what registry key the search process actually stops may help you find the product.

Possibly there is a virus or malware installed on your system
While not necessarily the case, a virus or malware may have a registry filter installed which blocks operation on certain keys to stop you or security software from removing it. Note that this behavior is similar to what many security products do. There may be a "me first" type of race going on your computer.