The PSU that I found is Unitec. It was installed, and the computer is booting, without issues. The optical was not installed, because the PSU came with an incompatible cable. I will buy an external optical drive. Thank you for your help. 
In the last few days, the problem worsened. Sometines, the back green led and the optical disc lights flashes once every five seconds. One time, I pushed the button next to the back led, and the computer powered up normally. But, after I shut it down, it went back to the flashing led. After disconnecting the power cable for 15 hours, this morning, the computer up normal, but after another shut down, it went back to the flashing led. Any suggestions? Thanks.
XPS 8910, Not booting