My guess is that app-locker is preventing Notes from opening. This can probably be worked around. NB I don't have app-locker installed but file searching shouldn't need it.

The next thing to worry about is, finding the data. If you saved the info to a file, can you remember the folder-location and the name of the file? If not, there may be a workaround because if it exists, it should be findable!

I'm assuming you can't use any software on your phone, is that correct?
If this is the case, plug the device into your PC, in mass storage mode, and see if you can browse the folders (app-locker may prevent this - not good!). Can you see your file? Notes files are usually HTML (.html or .htm) or plain text (.txt). If there's no extension but the name looks right, do "Open with Notepad". The folder called "N900" in the pc file manager is /home/user/MyDocs . You cannot (easily/at all?) access the files above this from a pc. To do so you need to use the N900's terminal, microB or a proper file manager (not the hand-cuffed Nokia one).

As to the passwords for app-locker - I suspect they're encrypted, but you may be able to find a way to reset them using the terminal, if you can run XTerminal?

** If you are looking for something like the file that appears when your pc crashes and you're working on a word-processing doc or similar (the recovery file?), then I don't think you're in luck. I think that if the information you typed was not physically saved in a file, it will have been erased either when the phone froze or when turning off the device. **
I may be wrong though.

However, a crash-dump is likely to be higher up the directory-tree than MyDocs so you would need to view it on device ... not possible ...

After all that, you've said that you've backed everything up so you could always flash your device?

Next time, write down the access codes & stick it somewhere safe!