This is moving to the "weird" territory.
The things I'd be troubleshooting would be:
- Amount of memory (RAM) available; get this info from the OS
- Amount of memory (Storage) available; get this info from the OS
- Whether ArcPad installed properly; perhaps view in File Explorer and browse and compare folders against an ArcPad that works (e.g. ArcPad on Windows)
- Whether ArcPad extensions are loading properly; About ArcPad > System Information
Hopefully you may be able to get some leads from the above.
If not, well, I hate to be that software engineer and say it's a hardware problem, but, it is starting to look that way.