Can't mount HD

Hello, total noob here.

I'm having trouble accessing my computers main HD through Knoppix. I can access any external drives I connect, but when I try to access my computers main drive I get the following error message:

The device /dev/sda2, is mounted.
Forced to continue.
Error opening partition device : Device or resource busy
Failed to startup volume : Device or resource busy
Couldn't mount device '/dev/sda2' : Device or resource busy
Mount failed.
Please check that the device is plugged correctly.

But when I look at the device it says it is not mounted. How can I get to being able to access the drive? Thanks in advance!

Are you trying to access and view the contents of a windows drive with ntfs filesystem?

Yes I am.