Dear @Smygou
First for the Vertex K8400 there’s no Power OFF switch.
If you want a ON OFF switch, You can add one like this: Vertex K8400 power switch by Zannddor - Thingiverse
For the problem with homing (loud noise before hit endstop), You can check this:
Also check for Printhead jamming:
=> The alignment of the printer head axis (cross) and axes X Y is not correct.
How to solve:
Make sure to install the printer firmly on a stable surface. If not, adjust the feet until the printer is stable.
Next, move the printer head back and forth, left to right with one hand. Make sure not to force, as you should be able to do this without moving the printer itself. If the printer moves while trying to move the printer head, then the axes are not aligned correctly and the printer head is jamming itself.
If the printer head jams when trying to move back and forth (Y axis), try and move the two blocks in- or outwards (1). This depends whether the opposite axes (2) are pushed in- or outwards at the Y-movement. Moving may require some force. See Picture below

If the printer head jams when trying to move left to right (X axis), try and move the two blocks in- or outwards (1). This depends whether the opposite axes (2) are pushed in- or outwards at the X-movement. Moving may require some force. See picture below

Best Regards,
Velleman Support