I had BOINC installed on D drive on windows and it worked fine until my D drive failed. I removed the drive and restarted. The BOINC client failed to restart (could not find files). I tried resintalling several times and even tried uninstalling. Nothing worked it kept failing trying to locate the D drive. I mounted a new drive and gave it the drive letter D and then I was able to reinstall.

I tried to search for config files, etc. to reset it's preferences but had no luck. Maybe there needs to be a "clean install" option?

It's a Windows registry problem. Use regedit, and navigate to

[HKEY_LOCAL_MACHINE\SOFTWARE\Space Sciences Laboratory, U.C. Berkeley\BOINC Setup]

You'll see two keys listed

INSTALLDIR
DATADIR

- either or both may refer to drive D. Change them to a valid drive letter, and the installer should run.

If you managed to salvage the BOINC data folder from the failed drive, put it at the new DATADIR location before installing BOINC - you might be able to pick up where you left off. Otherwise, just start over again.