As others have said, you should contact Kobo in case you have a defective unit.

Some advice for dealing with technical support:

Only bring up the most immediate problem. In this case, the most immediate problem is that the device does not turn on.

Don't tell them how you've tried to fix it. If they try to tell you something that you have tried, just do it again.

The reason is that most of the people who do support read a step-by-step process off the screen. Some are okay with extra details but I've found that a lot of them get impatient with extra details.