To add to what [NAME] already said, your procedure to clear BIOS isn't right... You should remove the old battery and press/hold power button on PC for ~30 sec, without any battery installed, and with PC's power cord unplugged from rear of the tower. Then install a fresh battery, plug in mouse, monitor, keyboard, PC power cord, and see if it boots now. BTW: What color is power button on PC when it won't boot? Is it steady or blinking? If blinking, count the blinks which are an error code.
I have an XPS 8500 with Intel i7 processor bought in 2012, and of course way out of service warranty. The system will no longer boot up. It has been running reasonably well for years with various upgrades - HDD converted to SSD, RAM upgraded to 32GB. No current changes to the system which could contribute to any issues. The normal boot sequence is configured to boot from CD first if a bootable media is there. There is no longer any discernable sequence. All that come up is the Dell logo accompanied by a progress bar that is permanently set at zero and never moves, with a text at the upper right-hand corner of the screen that says "F12 Boot Options". Pressing F12 does nothing - no discernable response. There is no other keyboard response other than to ctrl-alt-del, which has the usual effect of shutting it down. These responses are the same whether or not there is bootable media in the CD drive. There is no way to get to the 'BIOS' configuration screen. The green LED on the back of the power supply is on constantly while the system is plugged in. The yellow LED on the mother board is on constantly also, while the system is plugged in. The yellow LED on the mother board does not turn off or blink at any point. I have removed the coin cell battery, waited for 20 minutes, reinserted it, and rebooted by holding the power button down for 20 seconds or so. I have unplugged the system, again waited for 20 minutes or so and restarted. The response is exactly the same in both cases to what is described above.  This indicates to me major motherboard failure.  My questions are two. 1. Is there any hope; can the system be repaired? 2. If not, what are my options to get back to a similar state of functionality for my desktop computer? Thank you in advance for any advice.
XPS 8500, won't boot