[NAME] Liverpool  -  When was last time you replaced the motherboard battery? CR2032 3-volt coin cell battery.  See Service Manual for details.  I'd start with that, and while you're inside the case, blow out all the dust bunnies with canned air.
The last two days I have had problems starting my XPS 8900 When pressing the power button yesterday - I received the orange flashing light when attempting to start. After a bit of googling I found out that removing the power lead and all USB devices then pressing the button for 30 seconds would solve the problem. This it did. To be sure everything was working okay I shut the machine down and restarted again. Started normally. Just tried to start machine again today flashing orange again. Pulled out the power lead (did not remove USB devices this time as its a bit of a fiddle) held for 30 seconds and computer booted again and now appears to be working again.  I am wondering why this problem has arisen? Only change to the PC before the first problem occurred was installing and running the updated  Support Assist programme the day before it failed to start first time. Obviously I am getting a little concerned should the PC not start up at all. When it is running it is working fine with no issues.  Any solutions please?  For the time being I will leave the PC on.  My power supply by the way comes through a Schnieder UPS.
XPS 8900, orange flashing light issue