apple icon appears but ipad not responding then the icon disappears to black screen what do i do

Reboot the iPad by holding down on the sleep and home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider if it appears on the screen - let go of the buttons. Let the iPad start up.

If that fails to start the iPad, you will need to restore the device. Read this all the way to the end and take note of Recovery Mode. You may need it.

http://support.apple.com/kb/ht1414

If your iPad is still in recovery mode, just disconnect from the computer and restart your computer, then launch itunes and attempt to connect your iPad again. When you get his unknown error is there a number that follows it? Could shed some light on the error you are getting.

Here are some steps you can try to resolve this error let me know if you need help with them. http://support.apple.com/kb/TS3221

Have you tried another computer?