MISSING BOOTMGR

Sorry. English isn't my first language. I use Windows 11. Yesterday I was playing game on my computer when suddenly my system got stuck (crashed) so I held the power button down for a few seconds to reboot. But the system didn't start normally and instead now ok stuck in "bootmgr is missing"...

My desktop is a Pavilion p6-2143w. I found a google cashed copy of the specs here: http://webcache.googleusercontent.com/search?q=cache:esmgzxzxZkcJ:support.hp.com/us-en/document/c03349236+&cd=2&hl=en&ct=clnk&gl=us I tried adding a Nvidia 730 with 2g ddr5 but was stuck at the blue hp screen...