The first step in security is considering the physical security of the PC. Maintenance of physical security depends on the location and the budget. 
The second step is the factors related to physical stability that include the power supply, physical location of the computer, room temperature, etc. Failure of anyone of the above said factors leads the computer into risks.
There is a good chance that your home PC is one of the most expensive things in your home, or if you have got a laptop, it is likely to be the most expensive thing you carry in a bag.
Although your insurance policy may cover the costs of replacing hardware if it’s stolen, there is  nothing that  money can do to retrieve precious or personal data. So physical security is as important as software security.

Some of the methods 

Computer locks

Nowadays  PCs are available with a locking feature, which contains a socket in front of the case to unlock and lock the case. This helps us  to prevent unauthorized users from gaining access to the hardware of the PC, and also it prevents them from booting the system with their own floppy or hardware.

BIOS Security

BIOS (Basic Input Output System) are built in software, which describes what a computer can do without accessing the programs on the disk. It contains a code which can control the keyboards, monitor, serial and parallel communications and some other functions. BIOS comes with a ROM chip in the computer which ensures that it will not be affected in case of disk failures.
Setting BIOS password prevents the unauthorized users from rebooting and manipulating the system. This provides a low level of security as someone can disconnect the batteries and access the BIOS with manufacturer default passwords. However it takes some time for unauthorized users to open case and accessing BIOS, which leaves some traces of tampering.

UPS

A Continuous uninterruptible power supply should be provided to the systems in order to prevent loss of unsaved data during power failuresUPS (uninterruptible power supply) is used to protect against sudden loss of power.

• Sometimes sudden surges or drops in supply can also cause physical damage to computer components.
• The computers are plugged into the UPS, and if the mains power cuts out, the UPS provides enough power for the computers to shut themselves down and save all their information.
• Complete loss of power can cause the obvious problems of lost data and hardware damage.
• It is necessary to consider the size of the load that is to be connected to the UPS. The load may consist of a specific type of computer, workstation, mini-mainframe, hard disk drive, or test equipment.
• Once the equipment requiring a continuous power source is identified, the necessary rating of the UPS system can be determined by adding the volt-ampere (VA) rating on the nameplate of the equipment to be served by the UPS.

Tips for keeping your PC physically secure

• Always maintain a redundant power supply and also make sure that only authorized users access the computers.
• Use system’s screen locking functionality to protect against physical access, such as a screen saver that won’t deactivate without a password, or just log out of everything so anyone that wants access has to log in again.
• Enable the option chassis intrusion in the BIOS settings to be aware of unauthorized users.
• A continuous interruptible power supply should be provided to the systems in order to prevent loss of unsaved data during power failures.
• The systems should be placed in a room which is dust free and has a good ventilation to avoid overheating of CPU.
• The PC keys should be secured and not left unattended.
• Do not plug the computer directly to the wall outlet as power surges may destroy computer. Instead use a genuine surge protector to plug a computer.
• Check the system input power supply and grounding at least annually to ensure that it meet the manufacturer’s specification.
• Static electricity may affect the integrity and reliability of data and programs processed and stored on equipment, hence antistatic devices should be installed.
• Use gentle touches on the keyboard.
• Don’t eat food or drink by the PC.
• There should be no magnets near to you PC.
• Keep your PC clean.
• Lock the room properly in which PC is kept before leaving the home.
• Buy lockable CPU cabinet’s and keep them, locked