RE: XPS 8900 freezing
Have you looked in the Windows Event viewer for errors logged around the time of a freeze and your forced reboot? They may point you in the right direction.
Unless you have Win 10 Pro, you don't have downgrade rights to install Win 7 Pro. Win 10 Pro doesn't have downgrade rights to Win 7 Home.
Win 10 Home has no downgrade rights at all. If you have Win 10 Home, you'll have to buy a Win 7 license for this PC. And it's not legal to use a Win 7 disk from some other PC to install it on the XPS 8900.
If it were me, I'd go back to the exact original config: Disconnect the SSD and reconnect the 1T to SATA 0; remove all new RAM. Then boot from the 1T HDD to see if that works without freezing. If that works, then possibly your new RAM is incompatible (or just defective), possibly a corrupted or outdated driver, or maybe an SSD problem.
Keep in mind all power option and settings tweaks you made after booting Win 10 from the SSD won't carry over to the OS image on the HDD. So you may need to make the same changes, especially to USB and HID power management in Device Manager etc to see if those changes prevent freezing, assuming it freezes when booting from the factory image on the 1T drive.
Aside from mouse/keyboard, are any other USB devices connected? I've seen a number of threads with USB problems on this model that get resolved when those other USB devices are disconnected.
Forum Member since 2004
I am not a Dell employee