There are three things you can try.
#1: Power off the phone. As soon as you see the HTC logo, hold down the Volume Down button and keep holding it down until the Vivid vibrates twice, one short and one long vibration. If successful, uninstall the most recent app that could be causing booting issues due to being a malicious and/or incompatible application.
#2: Select RECOVERY, wait for the red triangle, then press and hold down Volume Up then press the Power button, select Clear /cache or whatever, and reboot the device. If all goes well, you're good to go. If not, see #3.
#3: This is if all else has failed. This will set your phone back to the "out-of-the-box" setting (factory reset). It does not wipe your Internal or External memory.* But you lose contacts, apps, and settings. First, download and install the HTC Drivers, located here:
http://db.tt/Pi0WLxUf. Then, download this HTC Vivid RUU (ROM Update Utility) from here:
http://forum.xda-developers.com/showthread.php?t=1564776. The RUU is in the first post. Once you have done all of the above, place your Vivid in Fastboot mode by making sure the phone is off, then holding down Volume Down and Power as you boot up the phone. You should see either ***LOCKED***, ***UNLOCKED***, or ***RELOCKED***. From that menu, select FASTBOOT. After you clicked on it, connect your phone to your PC via the USB cable. After a few moments, you should see FASTBOOT USB inside a red banner. If you do, continue. If not, retry installing drivers or wait for the drivers to set themselves up. Once done with all of that, open and run the RUU. Follow the on-screen instructions and in about 10 minutes, your phone should be up and running!
*If I remember correctly when I did it, it didn't erase anything. But I am not liable if it does erase something. So just in case, make a backup of your stuff.
Sent from my HTC Vivid Borked using Android Central Forums