HD has suddenly become unallocated

[bubblelegend]

I put in a second 300gb HD in a few months ago for data and everything was running fine, if a little slower. After defragging my main HD for programs, the second 300gb one now appears to be unallocated. It has all my data on it and I dont want to have to reformat for it to be recognized.
I'm not really sure what I should do. The same thing happened the 1st ime i defragged my main hd, but i just reformatted for it to be shown. I didnt think anything off it but it might have caused it even though i cant see why it should.
Any help will be much appreciated
Cheers

 

[bubblelegend]

yep its in the disk management sectionw where is says unallocated. If i get a better power supply would it revert it back to being healthy or would i have to reformat again?
Is it possible to regain the data on there. There was only about 30gig of data on it.
Also just to have extra back up, I'm tempted to get an external hard drive like the western digital 320gb premium on this site. Is it any good or are there more reliable ones?
cheers again guys

 

[bubblelegend]

Can anyone recommend good recovery programs for this problem?
preferably free?
would the data be able to be recovered onto a new external hard drive? to minimize the risk of it overwriting files on the existing hard drive
cheers for the help