my pc date and time changes when i start my pc . I update my date and time and when i do shut down and again turn on the time and date comes to a fixed date and time
Sounds like your motherboard's battery is dead. If your board is several years old it might happen. It is usually a coin-cell located somewhere on the motherboard. Does the BIOS forget all of its settings (ie does it boot to default?)?
+1 larkspur. Try replacing the really cheap, standard coin battery on your MB first. You can buy them in the grocery store. Here is one ref: http://www.computerhope.com/issues/ch000239.htm
Remember: RESET your bios to Defaults and SAVE after putting in the battery.