I just had a power supply fail on my computer. The power supply light would come on and so would the light on the mainboard but the fans wouldn't spin and system wouldn't boot. I always keep an extra PS around to test with, so I removed the cables that connected to the mainboard, propped the new PS on the side of the PC and connected its cables to the mainboard. Plugged it into the wall, flipped it on, pressed the PC power button and BINGO, the system fired right up. Your old acer might have a bad power supply.
The power supply is usually the fist thing to go on a computer and a flaky PS can cause all kinds of strange problems. I had a PC come into the shop that booted up and worked just fine with the mouse, but when you hit any key on the keyboard, it locked. I swapped out all the internal cards, RAM and nothing helped. I was thinking it was a bad motherboard but as a last resort, I connected another power supply and BINGO, it worked perfectly.
The first thing to do with your Gateway is to unplug, remove all the cards and the RAM, then reseat the cards and ram into their slots to ensure they are all making a good connection. You also might be having a heat issue with your Gateway. Remove the fan from the CPU heatsink and clean underneath. It's common for a layer of dust to buildup between the fan and heatsink and cause temp issues. It doesn't take long for the layer of dust to buildup and look like a piece of felt on top of the heatsink. Compressed air can't really get this off unless you remove the fan. Even after removing the fan, you still might need to use Q-tips properly clean the heatsink.
Bad RAM can also cause your PC to lockup and/or reboot. There free apps to test your RAM.
Incorrect BIOS setting can also be a problem but good mainboards can usually detect the auto configure the settings. Sometimes, the CMOS can get corrupted and you can reload to factory settings from inside the BIOS (or jumper the CMOS clear pins for a few seconds on the mainboard or remove and re-insert the CMOS battery).
It's really best to build your own PC using a generic case & power supply, then keep some spare parts around to swap out when needed. Sometimes, the only way to troubleshoot is to use the process of elimination and swap out parts, one at a time, until you find the culprit. Hopefully, you find the problem before you determine it's a bad mainboard (or a bad CPU). Modern CPU's rarely fail, unless they overheat. It can happen but they will normally shutdown before they fail.
Corruption in the OS can also cause the PC to reboot. Having a spare drive to reload the OS is useful, as well. Hopefully, some of these suggestions will help with your troubleshooting.
