This is one problem which I have faced for 3 years during my college days and I can safely call myself an expert in knowing why computers (specially the old once with old hardware) shuts down by itself. If your Computer is running XP, Vista, Ubuntu or any other Operating system and is shutting down on its, it can be for these 4 reasons -

1. Virus or Spyware - Is your computer new and has suddenly started behaving strangely from past few days ? if you get some message (not always though) saying your system is about to restart or any popup then your Computer is infected with virus. Many viruses edit registry of your system and make the computer reboot repeatedly. Get a good antivirus software and antispyware installed on your system and check your system fully. The best thing is take the hard drive out of infected computer and connect with other PC,make the hard drive secondary (do not double click on the hard drive icon or the virus/spyware will spread into host system too) and clean the hard drive fully.

2. Hardware Problem - If you have added new hardware and if you have faulty connection or loose connection, then too you can get your computer getting auto shut down after sometime, This happens alot with the bus not properly connected with motherboard or hard drive or CDROM. If you have added new hardware and feels the problem has started ever since, remove the hardware and see if it fixed the rebooting problem. If it does, then put the hardware again, this time, make sure all connections are proper and tight.

There can be some other hardware problems too like wrong power settings. To make sure you have got the correct power settings, do this -
[1] First of all go to Start Menu -> Settings -> Control Panel

[2] Now double click on the “Display” icon to open it. Next on the Display window, move to the Screen Saver tab (from the top section) and click on the Power button. Also you can direct open “Power Options” from control panel.

[4] On the Power Options window select all options as Never. Because, sometime the Stand By option set to 2 or 5 minutes and you assume that you System is down.

3. Heating Problem

For me, this was the case every time, I was using 4 year old computer and it suddenly started shutting down by itself due to heating problem. What happens is, CPU is covered by heat sink and as the heat sink gets old, its effectiveness to keep the CPU temperate low gets started affecting and as the temperature gets high in CPU, it make the system reboots. The simple solution for this is to get “heat paste” which you can get it for free from any Computer hardware store. Remove the sink and apply the heat paste on the sink and put it back though you can also look to buy a new heat sink, it won’t cost you more then $15. If you are not comfortable removing heat sink, take help from someone who knows this stuff.

4. Other Causes of Computer Shutting Down by Itself

* Another reason of computer shutting down automatically is a faulty SMPS. Due to power up/down SMPS often gets damaged. If you think that may be the case, change the SMPS and test it yourself or take help of someone who knows this hardware stuff. Also make sure the wiring connection with bus and power connection with SMPS is not loose.

* Sometimes mismatching of RAM speed can cause this problem as well. For example, if you are using a 533 Mhz RAM on one slot and 800 Mhz on the other then sometime dissimilar speed can shut down your computer after a certain load. If you want to add additional RAM, take your older RAM to the dealer and ask him for same speed RAM.

From my experience, I don’t think there can be any other reason of Computer getting shut down automatically in 10-15 minutes other then what I have mentioned. If you have something to share, please share it in comments. But here is a advice, if your computer is shutting down on its own, take it seriously as every time it shut downs, your hardware gets starts damaging including motherboard and harddrive.

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