To find out if you're a vampire, look for the vampirism trait on the skills page, and check your special attacks (the dragon on the adventure screen). I believe that vampires get a special attack (frost breath or something like that).
'Cause if healing is failing, you're likely a vampire.
Sorry.
As for reinstalling, Willow and Wyv have you covered. Save the appropriate files, and you'll be set. Typically, an uninstall won't remove any files you've added (like savegames), but they might... back 'em up to be sure. The reinstall might overwrite them as well... I've seen that logic before.