I've encountered something like this before. The garbled graphics point to a problem with the video card or PCI Express slot or maybe even the power supply unit.
Try re-seating the video card by uninstalling it from the PCI Express slot and then re-inserting it, to see if that solves the problem.
If re-seating the video card doesn't solve the problem then try a new/different video card.
If the problem still occurs with a new/different video card then it could be a power supply problem.
Hard disk drives shouldn't have been affected.