I already have data on my Toshiba external harddrive, but when I plug it into my laptop, a window comes up that says it needs to format. Will formatting it erase the information I have? It won't let me access the data on it.
If you already have data on the drive and it wants you to format then something is wrong.
It MAY be the main Hard Drive, however it may also be a problem with the circuit board in the external drive.
There are TWO ways to recover data:
1) Remove the hard drive and hook up to a PC via the SATA power and data cables (or PATA if it's an old drive). If Windows asks you to format again, then the Hard Drive is likely defective. Do NOT format until you try Step 2.
2) Use EASEUS recovery software or similar program (I used that to recover data off a failing, internal hard drive).
Either way, I'd rip the hard drive out. If it's still good you can buy an inexpensive case from Vantec at NCIX.
*If you can't recover your data then you should still run a diagnostic program from the manufacturer. If it says FAIL then unfortunately since you ripped out the drive you can't return it. If it says GOOD then you could run a FULL FORMAT on the drive and attempt to use it again.
(I'm not certain on how accurate the diagnostic programs are for hard drives. If it says FAIL it's very likely bad, however if it says PASS it may not be. Additionally corrupted RAM may also cause bad writes and you can verify your RAM by using MEMTEST www.memtest.org . If your RAM fails it may be due to defective RAM or your BIOS not having a proper Profile.)