protect PC

Level of protection depends on how much money do you want to spend on it.
Damaging peripherals:
- use a surge protector, or even better an on-line UPS (uninterruptable power supply), choose the one that has a connected equipment warranty that includes lightning strikes.
- If possible, don't plug the computer into the same outlet (or branch) that is used for devices with inductive load or devices consuming lots of power (like most "big" home appliances -  washing machine, dryer, cooler, electric stove, microwave, etc.)

Loosing data:
- BACK UP OFTEN! (This is the most important thing you have to do.) Depending on the amount of data you produce, get either a CD-R burner or a tape drive, and back up your data often.

Just to add to that, get a Virus Scanner and keep the virus definitions up to date.

Zaphod.

Also, make a backup copy of the installation disks of every software you purchase and store it in a safe place, apart from the originals.

I just thought of something else, but first in response to what joe just said:
While it is not a bad idea to back up all of your software, I personally have never had any of my CD's stop working, so if you already have a CD burner, then why not make copies. But, in my opinion, it is not worth going out and buying a CD burner just to backup your software. If you choose to use a CD burner for backing up data, then buy one and also back up your software.

The thing I just thought of was that you should make sure your computer is not overheating. Feel the side of the case after the computer has been running for several hours. If it feels quite warm, you might want to get another fan installed. Also, clean out the inside of your computer with compressed air every couple of months, and this should also reduce the likelyhood of the computer overheating.

Zaphod.

Z_Beeblebrox: Yes, you are right; however, If r_swaran chooses to use a tape instead of CD-burner, I'd still suggest making copies of install disks. Any decent computer store should do it for you on their burner for a small fee, provided the copies are made for backup purposes only (as specified in the license).
You never know what can happen to a CD - especially if you have little kids /pets around...

The ups that you use should have a plug for the modem also, since a lightning strike or where you do not have clean power because of motors ie air conditioners and up can destroy you system through the modem. This is the reason that uou see the major ones having this featurs.

As the first comment mentioned, it depends on how much you want to spend.  You could also invest in a RAID array, set up a cluster of two or more machines, hire security guards, etc <grin>.  
Seriously, if you could be more specific about what you want to protect (one laptop computer, a room full of servers, or something in between) and how critical the data you want to protect is (what is the "cost" of loosing one minute, one day, one week) we could probably make more meaningful recommendations.

Bert

bchew: nice idea about the security guards :))))

r_swaran: I thought the question was, how to protect the PC from _damage_, not from _unauthorized use_ ? Could you please be more specific?