Start with the Power Supply in the PC AND get a Surge protector if not already fitted.
Check the BIOS setting for what happens in the event of a power fail. If it is set to come back on, as all of mine are, then your system may be experiencing a power fail whilst you are out of the house, going into a reboot cycle and confusing the Windows.
Power surges might have gubbed the PSU, it happens a lot.
The external drives might be draining the board's capacity to feed USB and SATA Ports.
We used to build PCs, now we supply Dell hardware to all of our customers. Rather than trial and error to work out which cards conflict with which boards, we let Dell do that.