Plug in cable for power, press power button, remove battery, press power button again, remove power cable, press power button a few times 3+, put power cable back in, put battery back in, try turning on. If that does not work then you might have to take it in for repairs.
Check the power specs for your monitor at the Dell website. There are many. many Dell monitors.
To wake a Dell PC from power save mode using a wireless keyboard and mouse, first ensure that the devices are powered on and have working batteries. You can typically press any key on the keyboard or move the mouse to wake the PC. If that doesn't work, try pressing the power button on the PC briefly to see if it exits power save mode. If the issue persists, check the device settings in the BIOS or operating system to ensure that USB wake settings are enabled.
No
To save power
eat it
Hibernate is a power mode that allows the computer to save an image of the desktop to the hard drive and enter a state of reduced power consumption to save energy.
turn off power save mode
You can do it from Power Option in Control Panel.
Control Panel --> Power Options
The battery life on a Dell Inspiron 6400, 9 cell battery can last anything from 3h30mins to 5h30mins. The mainly depends on how the power saving mode has been set, when you reduce the computer's performance you save battery life.
70%
Hibernate.