On startup a computer goes through a whole bunch of checks to see if the vital Hardware (Motherboard chipset, RAM Modules, Video Card Controller, PCI Cards, etc..) are in working order, this process is called POST (Power-ON Self Test) . If all goes well then the Bios will run it’s mini OS and call upon the Hard Drive (or other booting device) to boot up your operating system.
Normally if all is well with your hardware, there will be a single beep (sometimes 2) and the computer will continue to boot, if an error or malfunction is found the bios will halt the start up and give Beep codes which unfortunately vary based on the Bios manufacturer.
To find out the type of bios you have on your machine you will have to open the computer and have a look at the mother-board, and look for the bios chip. The Bios Chip will vary in shape and size but should be easy to locate, normally on the board there are VERY small inscriptions telling you where everything is or a drawing of the board might have been put on the inside of the side-cover of your computer. Once you find out your bios model go to this site http://www.computerhope.com/beep.htm and check the beep error code related to your bios chip. Restart you computer and write down the beep error patern and check against the information on the site, you might need to replace something but the first thing you will want to do is to remove and reinsert the falty device (if it’s the case for that device) and try to boot the computer again.