When you put those photos on your computer from the iPad, did you do so via iTunes? Or, did you use the iPad as a USB and opened it with Windows Explorer (or whatev the Mac version is). If the latter, did you copy the photos or did you elect to "move" or "cut and paste" them?
If you moved them or cut/pasted them, then yes, you've messed up your Photos. The only way photos should be removed from the iPad is via iTunes or by deleting them from within the Photos app.
If that is what you did to put those photos on your computer, then I'm afraid you will have to "restore" the iPad to get it back to working properly. To restore it, connect it to iTunes and make a backup. Then, on the main Summary page, in iTunes, select the "Restore button. iTunes will do its magic and, when prompted, elect to "restore from backup" and select the backup you just made. Then, when all is done, your iPad should be just as it was (data and settings included).
This may save you a trip to the Apple Store (cause I'm pretty sure that this is what they will do). However, if you still decide to go to the Apple Store - do make a backup right before you go. That way, if they restore it (or replace it), you'll be able to put the backup on and carry on as before.
Sorry for your troubles.
Marilyn