Computer is made from parts: motherboard (main board ), ram (more ram can make work thinks faster at once), hard drive- hdd ( memory), video card ( hd is the best ( video card is separate only in pc computers, not laptops) ), and other not very important, like dvd re-writer, wireless connection, . If there are any fault you need to change one part, not a think in the middle of no where.  Any problems with any part such as the battery, fan, ram, wireless card, dvd or hard drive the unit will not boot. You should remove the cd, ram, wireless card and the HDD. With those items removed if there are no other problems your unit will boot as far as the BIOS and then prompt with a message saying there is no operating system. This would eliminate the motherboard as the problem. If your unit does not boot to the prompt you have a fan problem or a motherboard problem. At this point you would have to remove the bottom cover and try to boot while watching the fan for movement. No movement, replace fan. Movement, replace motherboard. It does boot to the prompt try re-installing the HDD and booting. If it won't boot then the HDD is bad and would need replaced and formatted with the original factory discs. If it boots with the HDD, try installing the ram and booting. Same procedure until you find the bad part. 
   Any error has solution, you need to read manual, all errors has explanation - simple, but sometimes expensive solution.
Because in hard drive is all programs and document, photos, you need to take good care of it. Don't smash and don't download any viruses. Visit only trusted sites, open only known emails, download only when you know what are you downloading, have a antivirus program. What ever happens to your computer until hard drive is safe all your document are safe to, which you can connect to other computer to get access.