Since no one else has jumped in here with a specific reason for your problem, I'll give it a shot. While I do have several Vertex radios (VX-180, VX-354, and VX-459 all three in both UHF and VHF), I've never seen that particular problem with them. I have, however seen a similar problem with their first cousin (Yaesu) radios.
I know you said your mic was new, but check to make sure it is working correctly. If you have another Vertex radio that is compatible with that mic, check it on that radio.
I've seen both the external microphones and the programming cables disable the keyboard and radio functions on Yaesu radios. The microphones usually turn out to be after market, and the programming cables usually are not plugged in correctly, but both can lock up a radio. Sometimes they even put the radios into transmit, and the only way to clear the transmit is to shut off the radio.
Hope this helps.
WA2CHJ