If you've forgotten the passcode and the iPad is now disabled then you will need to connect the iPad to the computer that you normally sync to and you should then be able to reset the iPad and re-sync your content to it (http://support.apple.com/kb/HT1212) - you may need to put the iPad into recovery mode.
And also if you just restore it you need to again enter the password
so you can fix this only by taking your device to the recovery mode
and then restore the device http://support.apple.com/kb/HT1414
To put the device to recovery mode press and hold the power button after connecting to the computer till you see a itunes logo
This solved my question
If you are trying to reset a disabled iPad from a different computer then (from here) :
If you restore on a different computer that was never synced with the device, you will be able to unlock the device for use and remove the passcode, but your data will not be present.
If your content (apps, music, films etc) are on that computer then you will be able to re-sync them to it, but presumably you won't have a backup on that computer from which to restore your apps content from.
You will have to download iTunes and log in to your account. To download iTunes, go to www.apple.com/itunes to download and install iTunes.
If you have an account, these are some simple steps to guide you through the snychronization:
1. If you have an account, the pop-up will appear if you did not sign in since the minute you got it. Sign in tohrough your account.
2. Check the iTunes Store and click Purchased, but if you have iTunes Match subscribed to your account, all your stuff will appear.
3. Go to Apps and a list of your previously installed and bought apps will appear.
4.Click all of them and resume to restoring them on your iPad 1, 2, Mini with iOS 6 (the latest iOS) or later, iPod Touch 4th, 5th Generation or later, iPhone 3GS, 4, 4S, 5 or later.
5. Press Eject to diconnect the appliance connect to your Mac or PC.
If you don't have an account, then go to https://appleid.apple.com/cgi-bin/WebObjects/MyAppleId.woa/wa/createAppleId?loca lang=en_US to create an account.