I recently pulled the hard drive from a laptop with a bad power supply, and have plugged it into my pc via a USB-SATA bridge. Both drives come from Windows 7 machines. Windows recognizes the drive as mass storage, but refuses to let me read it without formatting it first. I kinda don't wanna lose my data. Any advice?
It could be (assuming the drive isn't physically damaged) the partition table is corrupt. You can use TestDisk to fix this, as well as recover partitions and files.
Usually when we see this type of situation the system can see the drive but does not recognize the file structure, so it will ask you to format it. This may be the result of the drive being formatted through a serial header attached to the buss. Going through the USB bridge is likely an incompatibility for the system's ability to read the drive. - Formatting it would fix it as far as the system knows, and it would work just fine.
Your data is still most likely intact and can be accessed through a SATA interface attached to the buss. If you have access to a tower with that interface, try this. From my experience laptop power supply's are $20 on Ebay - no installation required.
In the old days I have slapped drives from one laptop to another, we are not supposed to be able to do this though it has worked for me numerous times. The system just needs to load a new set of drivers - Win7?
You may also have luck with a partition or recovery tool, there many available. I would give you a recommendation but it has been some time since I have played with one.
Hope this helps