Business PCs, Workstations and Point of Sale Systems

My otherwise reliable Z800 started having issues that seem to be accelerating lately.

Anyone else is having the same symptoms where it reliably shuts down after cold when getting into Windows; and then sometimes shuts down during normal operation? If so, what fixed it, if anything: replacement PSU? Graphics card? mobo?

Thanks!

Symptoms:

• reliably shutd down on startup from cold - either while getting to the login prompt, or right after loggin in
  • the shutdown is abrupt - i.e. an unexpected one, i.e. not OS-initiated. Nothing in the event logs.
  • don't remember it to ever shut down like that before it gets to the Windows boot process - i.e. never during BIOS set up
  • haven't been able to run hardware diagnostics from a flash drive or a DVD yet - just haven't gotten to it yet
  • the issue started about a year ago - preceded by having to press the power button twice before it powers up
  • if I let it sit at the BIOS boot prompt for 10-15 minutes (i.e. before it gets to the OS), and then startup - it goes through w/o a shutdown
• occasionally - and more frequently lately - shuts down during normal operation
  • 2-5 hours into uptime, while seemingly doing nothing unusual - reading and browsing - shuts down abruptly

The system:

• Dual 2.4Ghz Xeon CPUs, 18GB RAM, 850W PSU, Quadro CX, boot SSD, four 2TB drives in RAID5
• Windows 10 Pro