Oh no! Let's work on getting your awesome S4 to be more than a pretty flashlight again, JPG123. It certainly seems as if you're on the right path. Safe Mode is a great way to get into your phone and purge a few things. If it stopped rebooting when you did happen to get it into Safe Mode, that does indicate the reset you were trying should get your phone back to normal too. Sometimes getting into the recovery screen is tricky though, as it's not as simple as just holding the 3 keys you mentioned.
The phone has to be completely powered down to start with. Then you'll need to press and hold the Power button & Volume up key & Home key for quite some time. You'd let go of only the power button when the phone vibrates but keep holding the Volume & Home key until you see the Android logo. Once that little green guy appears, you can let go of all the keys. You'll need to use your volume keys to highlight and power key to select wipe data/factory reset, then Yes -- delete all user data and last but not least to reboot the system now.
Please keep us posted if that helps.
Follow us on Twitter www.twitter.com/vzwsupport
My phone is having this exact same problem. I have gotten it to the safe mode menu and done a wipe of everything to no avail. my next thought was to try and use the options provided here to redownload the drivers: http://www.theandroidsoul.com/drivers-installation-guide-for-samsung-galaxy-smartphones-and-tabs/
does this sound like a safe bet? is there anywhere i can get the drivers here?