I would seriously doubt this is anything to do with jailbreaking, but we'll see...
First of all you need to be SURE it is charged. The only way if it is dead is to use the WALL charger. Connecting it to the PC via USB just won't cut it. Give it a good hour or two connected to the original 10w wall charger that it came with...
Next, hold both power and home buttons for 10 seconds. Then release both and press the power button. The iPad should now start to boot.
Once you get to this stage tell us what happens. You should see the silver apple logo which indicates it is booting.
If you still see nothing on the screen or you see the red empty battery logo then you have had a hardware failure (assuming you have given it several hours of charging).
This is nothing to do with the jailbreak. The boot process of the iPad cannot be changed by software in any way. If that is the case you need to take it back to Apple for warranty repair. They will not be able to tell it is jailbroken if it cannot be turned on using the 10 second button method above.
Post back and let us know how you get on.