Lyngaas

The thing is the starter motor is not even turning over when the car aint working. Slack earth/power lead, well. Where should i start to look?

Hello. We have an 2006 C8 2.2 HDI and we are experiencing intermitten starting issues. First time we noticed it was a week ago, it simply clicks and you can hear a loud click in the engine bay but engine is not turning over. Then i waited a little bit and tried again and it fired right up. Today i got the same issue and i had luckily parked on a hill and could start it by rolling it, it was also a bit hard to start when i left work but managed to get it running. What happens when it wont start is that i hear a loud click in the engine bay but the starter aint turning over, then u wait for 5-10 min or more and then suddenly it fires up like usual. We have two keys and both work and then suddenly dont work. Does anyone have any suggestions towards what this could be? Could leaving the key in the ignition for longer before attempting to start remedy this(reason im asking is incase the ECU could take a longer time to read the code from the key). Thanks in advance for any help. -Lyngaas