Our 8 yr old compact desktop PC has crashed and I can't re-start it

it can be very slow at times and I've had a good clean out and it's been ok, but very occasionally if will just freeze and you have to hold the on/off button for 5 seconds to close and then re-start the PC.
When I do this is comes up with options to start in safe mode, start in safe mode with command prompt, start windows normally (which I always choose) and it's fine after that

However I did exactly that earlier tonight (Friday) and got the 'Windows Boot Manager' screen up with the following message.

Windows failed to start. A recent hardware or software change might be the cause. To fix the problem
1. insert windows instillation disc and re-start your computer
2. choose your language settings and click 'next'
3. click "repair your computer"

If you do not have installation disc, contact your system administrator or computer manufacturer for assistance

File:  \Windows\ system32\ config\system

Status: 0xc000014c

Info: windows failed to load because the system registry file is missing or corrupt.


I cannot get past this screen to windows 

I've not made any hardware / software change recently, so that's not the problem and unfortunately i do not know where the installation disc is.

is there anything I can do myself to get windows up and running again, or do I need to call someone like geeks on wheels to help??

any advise would be appreciated!

wife and I have an Macbook and plan to transfer everything over to that from the main PC, but wife is spewing at the moment because she doesn't want to lose her MYOB files on the Compaq