I booted ReactOS 0.4-RC1 on my test PC with RosDbg communicating to a host PC via a null-modem serial cable attached to the COM1 port. When the test PC finished booting, I bugchecked the test PC with TAB-K. On my host PC I entered set condition * first always. Then I entered cont so the test PC would continue. I inserted a floppy disk in drive A. Then I started ReactOS Explorer. ReactOS Explorer tried to read the floppy. The drive access light came on then the screen, mouse, and keyboard froze. The drive access light remained on.
I was able to capture a backtrace with the host PC. I then entered cont so the test PC would continue. What happens after that may be interesting but is not related to the bug I am reporting.
A debug log that begins when the test PC's boot finished is attached.