Computer shuts off - looks like hiberantion. Flashing Blue power button every second?

Hibenation mode not enabled.

Switch off completely at mainpwer supply - then sometimes wony start again for some time.

Any help

Make, model, operating system?

Sounds like could be going into standby mode.
The flashing power light rang some bells as my laptop does the same in standby.

Check your power settings to see if it is set to do this after a period.