How to make Finder display correct ‘today’ date

If you don't mind using the terminal you could try this:

find . -type f -exec ls -lth {} +

This will list files from current directory and all directories below, sorted by modified date. A variant not listing modification date would be:

find . -type f -exec ls -t {} +

But I believe that it would be better to just list the files that have changed the last 1440 minutes

find . -mmin -1440

Run /Applications/Utilities/Console.app and check system.log.

Look especially for entries that say something like disk4s3: I/O error. If you see that, then your hard drive is failing.

Since you did a re-install, I assume you have everything backed up. If not, try to cool the computer down as best you can, either by raising the fan speeds or even putting a cold pack under it, and perform a backup.

The following article has detailed instructions for how to limp the drive along or possibly restore it: Hard Drive Recovery. But if you already did a clean install and are still seeing I/O errors in the logs, it is most likely not recoverable.