if device cannot power on what should I check?

Hi @yokewenghong

With a power adapter connected, check if the Standby LED on the motherboard is on or not.

See item # v on p.20 (p.18 of 51 pdf) of the technical product specifications manual, for the location of the Standby LED

If it is not on it may be a faulty DC-In jack (example only to show part) or a motherboard problem.

Regarding the DC-In jack, what can sometimes happen is the +ve centre pin of the jack breaks internally, opening the power circuit. If this is the problem then the jack will have to be replaced as it cannot be repaired.

If the jack is OK i.e. supply voltage gets to motherboard through the jack OK, then you'd need the motherboard schematics to find out where and what the problem is.

What is the make and model number of the motherboard, (printed on the board itself)? Sometimes searching for (insert motherboard make and model number) schematic, will find them if they've been made available by the manufacturer.

If it is on, it may be a faulty Power button, a possibly corrupted BIOS or a motherboard problem.

For a possibly corrupted BIOS, try removing the power adapter and then disconnecting the cmos battery¹ cable connector from the motherboard (see Item # j for location) and then press and hold the Power button operated for a full 30 seconds and then release it.

Reconnect the cmos battery cable, reconnect the power adapter and check if it turns on OK.

¹ When the cmos battery is disconnected, use a DMM (digital multimeter) to measure the battery voltage on the red and black wires of the cmos battery connector cable. If it is <2.5V DC or if the battery is >4-5 years old replace it. Here's a link that may help if it has to be replaced.