Retrieving data from a previous computer's hard drive

Hello, I have read the forums and there have been posts about this but none of the solutions work for me. I had a computer whose motherboard and CPU died. I bought a new computer. I am now trying to access the data from my old computer's hard drive. I have done 2 separate things. First is getting the external Hard Drive bay and using the USB plug to attach it to my new computer and access the old hard drive. After that I tried physically installing it into my new computer. Both options resulted in my computer correctly identifying and recognizing the hard drive, but if I try to access it in any way, I am immediately prompted to format the drive in order to access it. This obviously is a problem for me, as I want to get the data off the hard drive and formatting would wipe all data thus defeating the whole purpose of me accessing the drive at all! My OS is windows vista home premium 64 bit, any help would be greatly appreciated. Also the hard drive in question is a SATA Western Digital 320GB and was the main and only hard drive on my previous computer (using windows vista home premium 32 bit), it was not a spare or anything like that.

It has nothing to do with security... he's not getting "Access Denied"... he's getting "You must format this volume to use it". I would suggest running chkdsk on that drive to see if that corrects the errors in the file system. If not, then you'll have to put the hard drive back into the original computer in order to pull any data off of it. You could also try booting from that drive in the new computer... but that likely won't work.