Original post (clipped) <<<I've been using Win XP with AMD Sempron 2800+ processor, 512 MB RAM & 200 GB harddrive sucessfully for the last year. Now all of a sudden when trying to power up, nothing appears on monitor and computer shuts down after only 15 seconds>>>> Hi, there could be many,many reasons BUT on the other hand being only a year old system we can possibly narrow it down. (1) check the cable connections between your hard drive and motherboard. (2)check/reseat the RAM sticks (3) when you unplugged the monitor, did you get a msg on the screen to the effect .."cable unplugged..."?? (4) do you know whether you have "on board video" or a "seperate video card"?? NOTE: all the above suggestions assume you are comfortable working inside the system (you have changed the power supply...). IF NOT pl post back for further assistance. good luck---Venkat PCBUILD maintains hundreds of useful files for download visit our download web page at: http://freepctech.com/downloads.shtml