Why do you have to turn off Xbox 360 before removing Hard Disk Drive?

Because it might be reading and writing to the drive when you interrupt the power and jerk it out.

Will the Data from the Drive gets corrupted if doing it multiple times?

yes and you can damage the drive too, the platters inside will still be spinning when you pull it out.

Because it might be reading and writing to the drive when you interrupt the power and jerk it out.

Hello Kathryn,

Thank you for posting here on the Xbox forums. Are you able to skip sign in? Is there a removable hard drive in your Xbox 360? If so, we need to test if the hard drive is corrupted in any way. Lets try removing it as a troubleshooting step. Make sure you
console is turned off and unplugged before removing the hard dive.

You can check this link out to locate where the hard drive would be located on each type of Xbox 360 : Add or remove an Xbox 360 Hard Drive

Turn on your console without the hard drive. Let us know the results

Hey there M0NOXiDE,

Can you try re-seating your Xbox hard drive for us?
Make sure you turn your console off before you attempt this.

This guide shows you what to do:
http://support.xbox.com/xbox-360/settings-and-initial-setup/add-remove-hard-drive

Let us know if you still have problems. Thanks.