The main reason to try Safe Mode is to narrow the problem down to either something you installed or something with the firmware or hardware. If the problem goes away in Safe Mode, then something you installed is probably interfering -- but it can be hard to further pinpoint the culprit after that, apart from uninstalling apps one by one until the problem goes away.
If the problem persists in Safe Mode, then it's more likely an issue with the firmware or hardware. You could consider reinstalling the firmware, but with HTC devices, that may require rooting.