If QCAD cannot find its resources (help files, fonts, hatch patterns, translations, ...), it is very likely because it is not being started from its installation directory. Please change into the installation directory of QCAD first and then start QCAD from there:
If that does not fix the problem, you can indeed reinstall QCAD by extracting the downloaded tar.gz file again. Your CAD drawings are unaffected by this. However, backing up your data including CAD drawing files regularly is strongly recommended anyway.