bootmgr is missing

please identify the operating system you are using...  example. xp or vista or windows 7

look here how to fix it :  http://www.howtogeek.com/howto/windows-vista/fixing-bootmgr-is-missing-error-while-trying-to-boot-windows-vista/

note that it may be caused by hardware failure...

Savant is correct because it can be a notification of a hard drive failure. If your running xp there is a couple of different things you can try

1st get your home pro or what ever version os cd and boot to it, then press R and load the recovery console. From there type C:. then type fixboot (enter) then fixmbr (enter) then restart

2. boot to recovery console, C:, bootcfg /r, select your windows installation and press enter

3. Boot to windows cd, press enter, keep going through the windows until you see a screen that says windows detected a different version of windows would you like to repair it.

ps make sure you have your product key
do not format

Insert a bootable operating system  cd into your drive what you have earlier in HP 6445B.
Boot using the cd and just  reinstall the operating system.

if i doubt the hardware - i run diag on Ram and disk -to be sure about the basics..

I also recommend running chkdsk /r from the console

running a diag is different than chkdsk - which may ruin your disk...

http://wp.me/p2IqIP-35