I got the dell studio xps 435mt in 2009. in the fall of 2013, i noticed one day that the computer would not startup when i pressed the power button. I waited a couple days and tried again and it did start up, ever since then, getting the computer to turn on was a battle, I would unplug and replug the power cord over and over again, unplug and replug the cat5 cable from the NIC because for some reason it would sometimes help start the computer. I've been doing this the past 2 years and getting by, sometimes it would start immediately other times it would take dozens of attempts. Finally in sep of 2015 i couldn't get the computer to turn on after an hour of trying the above. I noticed the green light on the back panel of the power supply was much dimmer than usual. I've also realized based on prior experience, that my chances of starting the computer seemed to depend on the brightness/steadiness of this green light on the back. So i read a bunch of forums and threads about difficulties getting the dell studio xps 435mt to turn on and a lot of people said a new power supply was the answer. I went to best buy and got a 520 watt insignia power supply. It is a tighter fit in the case compared to the factory installed 350 watt power supply but it fits perfectly fine. No problems attaching the 4 rear screws of the power supply to the chassis either. I think the easiest way to install the new power supply is to start with the 8pin motherboard connector then plug in all the remaining connections first(except the top cd drive) before trying to fit the power supply in the chassis. Then position the power supply in the chassis and then plug in the top cd drive. A number of people have said the reason the power supply fails is 1. computer power supplys lose power as they age and 2. a 350 watt power supply is underpowered for the dell studio xps435mt. After all the connections were made, everything powered up no problem. I shut down and powered up again to see if there would be any issues. There were none. Additionally i've noticed that some of the usb ports that didn't work before, work now, i imagine because they were insufficiently powered. I manage to squeeze out 6 years from my factory power supply, not bad considering typical lifespans of pc power supplys. If you're experiencing similar issues with your computer, I would suggest that you don't need to test your power supply or motherboard or power switch, just get a new power supply with more wattage. Make sure the replacement power supply has 1. an 8 pin or a 4+4 pin motherboard connector(the 520watt insignia is a 4+4 connector). the other connectors (24 pin motherboard connector), hdd, disk drive and graphics card connectors are pretty standard. When you remove the old power supply and install the new one, be sure to touch the computer chassis periodically to discharge static electricity. Also note the shape of the motherboard connectors as they fit only one way(some have rounded edges some are square). The new power supply only cost me $50 to bring life back to my computer so I'm pretty happy about that.