[Nickles]

hmmm... i just re-read your post.. i had assumed it would just cycle soft-resetting, not letting you actually boot up.. when this happens. when the phone can't boot regular for 3 times in a row, you will be prompted for safe mode.
but you are saying if you open an actual program and then try to close it, it errors and soft resets..
seems to me there is some leftover junk in the reg from either HTC or Mobile shell.
you could try tinkering around with the registry under HKLM/Software/HTC and see if there are some leftover settings that there..... or if your not comfortable with that, grab a program called 'Memmaid'..
there is a section in there called 'installed programs', where it queries your entire device for things that have been 'installed' - then displays all the areas in explorer, AND reg entries, those programs have installed themselves into.. awesome for 'cleaning' up bad/old registry entries..

however, a bit of advice.. don't spend too long on this, as it sounds like the phone is still 'new'.. before wasting your time, consider a hard reset, as it just might save you the headaches.. i have WAY too much time invested in this danged phone now, to even THINK of a hard reset.. so another bit of advice, when you are back up and running the way you want to, pick up SPB Backup, and do a backup of your system data..
this way, you can do a quick and simple restore from that point, next time you (and trust me you will) hose something..

good luck!