XPS 8900, 460W PSU, have to press power botton twice to start

a dying psu would make power button harder and harder to press and turn on pc.  at this point first try replace cmos battery w a new one then clear cmos by motherboard CLR CMOS jumper

@redxps630​ what are the anacromyms cmos, clr jumper? Sorry, I'm an amateur. Thanks

A desktop's CMOS (Complementary Metal-Oxide-Semiconductor) is a small memory chip on the motherboard, powered by a coin-cell battery (like a CR2032), that stores essential hardware settings, the system clock (date/time), and boot order, ensuring they're retained even when the PC is off. When the CMOS battery dies (typically 2-10 years), the computer loses these settings, leading to wrong times, boot issues, or lost configurations, requiring a simple battery replacement to fix. Clearing CMOS (resetting the chip) is a troubleshooting step for boot problems by restoring default BIOS settings. 

@redxps630​ thanks alot.  now i'm aware. issue resolved

Genuine Dell XPS 8900 Power Button Assembly 7R574 07R574. Is this the correct replacement switch? I thin k it is. thanks

@redxps630​  I removed battery and then cleared cmos by motherboard CLR CMOS jumper.

now the computer starts as soon as I plug it in. The power switch won't turn the unit off and the computer screen does't connect...light up etc. Thanks