Hi, Hrd... Try open top casing of system unit and check connector of screen and logic board, maybe it's disconnected. Second: Have you saw any picture in dim on screen? If exist that mean 'back lamp' is faulty. Just replace it at stall has expertise and part to install it.
Here i'm giving a one reason why it happen. Might-be problem occur at main key kit. In internal kit was oxidize. In cool weather the connection is fitted but in hot weather the it's out-fitted. Try service your key's kit in car.
Recheck your adapter output voltage using volt-meter and check the spec of adapter on their label. If the output too below (<< 19 volts)dan not enough currents deliver to logic board. Or the adapter cable is half-crack (just small amount of current-Ampere can through via the cable). Try use another adapter. Other reason maybe the CPU fitted not properly, don't tide CPU's skrews hardly.
The hard disk controller is faulty. Do touch on hd controller (locate bottom of the hd) with finger, if feel hot in short time mean that chips is burning. If the controller damage, computer con't detect it's specification. The arm of all hard disk is no problem. The problem come from 'read/write head'is disconnected from edge of arm when it park long time on disk. Don't OFF your computer more than one month in time to avoid this phenomenon happens.
You need to do the major servicing. If still unchanged, the logic board (DC-DC converter) is faulty. Like maintain a car, there are 2 type of services. Minor & Major services. Minor service just check or replace like battery and outer dust. In major service, must dismantled and check all part of a system, remove all internal dust, replace all half-faulty components and so on.
Try pull-out the main battery and switch-ON the computer. If the system still OFF mean the adapter(or adapter cable) or the DC-to-DC converter faulty. If this occur,it (DC-DC Conv) can't charged main battery and can't deliver current to logic board from adapter. DC-DC Conv + Battery act like UPS.
To know either hardware or software faulty, just pull-out the hard disk and switch-ON the computer. Display the BIOS setting for a while. If computer do hanging the problem came from hardware (logic board). If not the problem came from hard disk (software) or hd itself was faulty.
On Software: First, make 3 partions on harddisk. Second, do housekeeping the OS Registry. Third, delete ALL the temp files, the zero files and the zero directory. Make free 1/3 free space on hd. On Hardware: First, Add main memory. Second, Replace Hd with better RPM the computer can accept.Third do main service on CPU cooling Fan & sink. Zaabar Zakaria