I've seen faulty hardware that will cause the post screen to stay on for a very long time. Remember that post is an acronym for "Power On Self Test" so if something fails that, the bios will get stuck there on that screen
Try disconnecting everything from the board like the hard drive(s) any un-necessary pci or pci-e devices including the video card if you can. Try only one memory stick at a time on a different slot each time. Disconnect all the usb headers on the board and remove any thing on the I/O ports on the back. Try a different keyboard and mouse too. Then only connect the bootable usb and check. If that works then try just the windows hard drive....Power down and disconnect the power cord each time you re-connect something and be sure your draining out the caps after each shut down and ground yourself before you go back in the pc. continue re-connecting things until your run into where it gets stuck on the post screen.
If you disconnect the hard drive, you should get a screen that states "no bootable device" after the post screen. If the post screen stays on after you connect the hard drive, then try that hard drive in a different pc and see if it locks up on that post screen too.
