Hi Mikgel,
It seems to be an issue with loose connectors. I would suggest you to run the Dell Diagnostics to check the hardware functionality. Power off the computer -> restart the computer, press 'F12' key on the Dell logo -> Select ‘Diagnostics’ from the boot menu. Please refer to the link if any error code shows up http://dell.to/OUGnqT
Alternatively, you may try to swap the power cable and SATA cable with the optical drive connectors.
Please ensure that the system to be placed stably and is not to be moved too much.
Please reply if you have any questions.