Aside from pulling power cables from a Dell server or blade, there are some other ways to (soft-)reset a frozen iDRAC.
Each rack server has an i-Button on the front panel of the server. To soft-reset iDRAC, hold down this button for 20 seconds.
If you still can log on using SSH, you can also reset it that way, saving you a trip to the server room. See the last part of this article to see how to do this.
To reset the iDRAC on a blade, you can log in on the CMC to do so.
From Chassis Overview, click Troubleshooting, then click on Reset Components (the third item in the submenu, next to Diagnostics).
If you cannot log in using the web interface but still have access to the unit through SSH, you can log in to it that way to perform a soft reset. Using PuTTY or some other SSH software, connect to the IP of the iDRAC using the root account and password.
Once logged in, type the following command to perform a reset:
racadm racreset soft
It will take a few minutes for iDRAC to restart and come online.
If you have DRAC tools (part of OpenManage) installed, you can also do this remotely:
racadm -r <ip address> -u <username> -p <password> racreset soft