These are the possible causes of a BC 50 Usual causes:
Defective hardware (particularly memory - but not just RAM), Faulty system service, Antivirus, Device driver, NTFS corruption, BIOS
May I suggest, that since CI.dll, also is noted, it mabe that the .dll is corrupt or missing. This is what must be done.
If you have a Vista DVD, you can make a repair install.
If that does not work or you do not have a Cd
You must test
Memory, Hard drive and BIOS.
To do so, you may be able to boot from Ubuntu. How To Back Up Data From Computer That Won’t Boot
If you can get Ubuntu to work, we know it is not a hardware related problem.
If you cannot get it to work, it sounds like hardware. Nothing that I can do to check the components, if you cant even boot.