"operating system not found"

Running windows 7, i downloaded gnome 64-bit, tried using the unetbootin software but it freezes on extraction at 39%, decided to just try extracting the files to my flashdrive (4gb, FAT32 by default) using PowerISO which i am familiar with however when i reboot my computer i get an "operating system not found" error.

any ideas whats causing this and what im doing wrong?

That's clearly not the way to make a USB install, I suggest you follow the official Wiki guide or try other tools suggested on the forum.

im running ubuntu and my system is also 64 bit and i installed BT onto my 8GB usb exactly as described in the guide and had no problems.
but when i try and boot it up it also says 'operating system not found'
i have tried this a few times, on multiple usb's and always get the same error!
any help would be appreciated.
thanks.

So you followed the Wiki guide ?
In case you did and it did not work I suggest you try the same USB on another machine, see if that works.