PMail v4.8 on my Windows 10 has totally locked up. The start screen hangs and program does not respond. I think I need to uninstall and re-install. Can this be done without loosing my address books and contacts?

The Pegasus Mail program files exists separately from its configuration and data files. Problems like what you describe are normally associated with a configuration file. The importance of that statement is that a reinstall overtop of the existing installation will not touch the data. Unfortunately it will not touch configuration files either so is unlikely to solve the problem.

Start with a cold boot of the PC if you haven't done one since this started happening. Not just a restart but a full shut down.

When the start screen hangs, is there any notice or can you tell what stage the startup was in based on what is shown in the lower left of the start screen. A hang at "opening new mail" is fixable.

Let us know of anything that comes to mind that you did prior to the problem (eg: a configuration change in Pegasus Mail or in the operating system, or a hardware change).