So your Cool-er froze on the grey gradient screen that you normally see when you turn it on?
Yeah it happens, and is a known issue. If you have the orignal firmware that Cool-er was released (pre v1.12.6) with this is a common problem. Good news? They seem to have managed to fix it in later versions of Cool-er firmware.
If you have tried powercycling and resetting it using the little reset button the back it might be time to go for the firmware update.
For the latest firmware. You will need a SD card in order to do the firmware flash, apparently you can't do it through the USB cable at this time.
If your Cool-er still does not boot up properly at this time you may need to contact Interead about the problem.