Root Desire HD stuck on boot (blackscreen) and cannot mount SD card

[scotty85]

Im getting no phone signal at all, when i try to change network settings with the new sim in, it says your sim could not connect to this network, but the sim works in other phones, it seems strange

hmm,not sure about that. what network is the sim for? if the phone did not ask for an unlock code with the new sim in,it is unlocked. you might try calling that sims carrier and see if they can walk you thru any troubleshooting steps.

aside from that,try toggling airlplane mode,and give the phone some time to find the new network. sorry i dont have much better advice,i will keep pondering it