ok i have encountared the exact same problem (unmountable boot volume, black screen + mouse cursor, etc).... but i have found a solution for those people who do not want to format, remove or replace the harddrive
1-First put the windows installation disc inside your computer, and set the priorty to boot from disc
2-When the computer says press any key to boot from disc (PRESS ONLY F8) and keep on pressing it until you see the advanced options (NOTICE that THESE options are loaded from the disc, because i have tried the advanced options without the installation CD, but unfourtunatley nothing worked)
3- Choose safe mode (TRUST ME THIS WILL WORK) but the computer will not go to windows... rather you will see it loading the cd windows installation
4- When Safe mode loads press next then press repair your computer... (AT this state your computer might run very slowly but be patient)
5- Now wait until your computer loads... and press next again... and this time you will see the options like ( Startup repair, or system recovery, or..... )
6- Choose command prompt and type bootrec/fixmbr
7- than type chkdsk c: /r (this option will eventually fix your computer, but it will take ALOT of time depending of how much your hardrive is corrupted, and it might stop at some point. If you feel that it is stuck at a specific sector, dont worry clos command prompt and repeat steps 1-7) and it will definetaly work