Pc not starting (by 4 users)

try swoping the power supply if you have a spare ,and if you cant do that test your power supply on another pc . its very common for a atx power supply to do that mostly after not booting up for a while . just try the above it should give you direction from there onwards

Sounds like a bad power supply. Although first I would check it over by unplugging Every Card, Hard Drive, even Memory, (mainly anything that is connected into the Motherboard), One at a time usually is best, as you may find a faulty card, or bus, run the Motherboard strictly off the Power Supply, If it then seems to run correctly, try pluggin just One thing back in at a time, (memory, then Hard Drive(s), then cards, Video-LAN-Modem-Sound/etc.

This should give you a good feel for what/or where about your system is failing.. Good luck, A good standard size Power Supply Unit nowadays is about 600W+, a lot of systems we get from the stores, or online will come with just 400W+,.

Again, Good Luck, and Happy Holidays!
Let me know how this works for you.

~G.