Why won't my HP computer stay in stand by mode

Why won't my HP computer stay in stand by mode? It goes to stand by briefly then automatically restarts.?

My HP Pavilon a1209a with a Celeron D and 512 MB of RAM will not stay in stand by mode. It stays in stand by for approximately 5 -10 minutes and the automatically resarts. And if I happen to catch it while still in stand by mode and manually wake it (by hitting the keyboard, moving the mouse, etc.) then it also restarts indtead of just "waking up." Is this a condition that requires a service technician? Thanks!

Solution:-this is a typical problem. your systems bios/cmos may be set to wake up on the LAN (ethernet or other network connection).. before going to your systems bios to test this is the case try disabling or removing the network connection before you put the computer to sleep or stand by.
if the computer goes to standby then you have to go to your system bios and disable the wake up on lan or whatever your bios has that option listed as. different bios means it is labeled differently.
the only thing a tech would do is do the tests above.
also if you have a screensaver set to start after 10 minutes of inactivity in extremely remote cases this can cause the system to wake form stand by.
or maybe your desk is not as secure and permenant as you think and your system is detecting mose movement (by the wind or other means) which restarts the system. the only thing you can do is trial and error to see what the actual cause of the problem is. you could get a technician to your location but the tech will only do as i've advised you to do. and a tech could charge you £10 to £100 per hour and it could take upto three or four hours to diagnose the problem using the trial and error method that even a seasoned technician would employ as it is not necesarily a hardware or software fault.
you need to also check your settings under power schems or what ever your system is set up as (your operating system).