When you boot it up with just the mouse connected... and it shows the main (but frozen) desktop... does the time and date appear to be correct? if not, is it always the same date and time when it reaches this point?
If you have no floppy in the drive and disconnect the hard drive, do you get the floppy icon with the question mark? If so, does it blink?
I assume it is not switching between the main and alternate video buffers and that is why it appears the screen is frozen and has no cursor... and since you mentioned the ADB symptoms as well... i would check around UK11 (Via 1) and UK4.
If you happen to have a digital multimeter with a frequency counter or a standalone frequency counter.. i could check pins 1 and 2 on the UK1 (should be 1herz and ~32kiloherz respectively). Also check for +3 between pins 8 (+) and 4 (-)
If you have no floppy in the drive and disconnect the hard drive, do you get the floppy icon with the question mark? If so, does it blink?
I assume it is not switching between the main and alternate video buffers and that is why it appears the screen is frozen and has no cursor... and since you mentioned the ADB symptoms as well... i would check around UK11 (Via 1) and UK4.
If you happen to have a digital multimeter with a frequency counter or a standalone frequency counter.. i could check pins 1 and 2 on the UK1 (should be 1herz and ~32kiloherz respectively). Also check for +3 between pins 8 (+) and 4 (-)