I'm just bought my Maxtor PORTABLE HDD a couple of months ago.
W/ this portable I'm feel so comfortable to keep all my personal data here & there. But suddenly today when i try to open it while its already connected to my PC the sign 'Access is Denied' pop up. Usually it will become autorun as well.I've tried uninstall USB Controllers through System Properties > Device MANAGER > Universal Serial Bus Controllers but it still happen. While I'm try to check it by OS Vista, the system asked me to format it.

The problem is all my important data was INSIDE that drive.... Try to see if you can access it on another computer.Was it prematurely unplugged without using "safely remove hardware" ? ?
Does it show up at all in Disk Management ? ?
To get to Disk Management right click My Computer and select manage then disk management...
Right click the drive and select properties.
Post back with your findings.

If it says raw your data is gone...Can we use System Restore like we did usually onto our PC?ermmmm maybe not possible to apply it i guess.
Yesterday i already gave it to my IT officer, hopefully he could help to fix it. I'm going to share here whats an exactly the problem & solution it is soon when he come back. Make sure you tell us exactly what he says and make sure he does nothing to the drive until we know what the problem with it is.System Restore only works on the Windows drive/partition and only AFFECTS Windows System files.
But do let us know the outcome...