It all started when I tried to install KAS internet security 2012 which I bought, I couldnt do a full scan with it without the scan freezing the computer after about half an hour so I was told by kaspersky support to install SP2, so I tried to from the microsoft website and I got an error similar to the one mentioned in title (Error at start !! 0xc0000034 !! 145/61825 (_0000000000000000.cdf-ms) ) and had to do startup repair to get past it and so I tried again from the microsoft automatic updates a few times and then I got a similar error but it would not go past that, I tried startup repair, kaspersky rescue disk (to do a full virus scan) and even set it into deepest scan, memory diagnostics, safe mode,safe mode in every form, more or less everything that comes up when you press f8 at start, tried to restore it to an earlier date in time when windows last worked fine and the same old thing, I did disk check in every different way you can when using command prompt to do it and then it changed to the above mentioned error. I know the simplest thing to do is reformat but as I have LOADS of work documents on this computer I cant risk losing them, I had to do a rescue thing a few years ago on a older computer but it renamed all my documents and files into numbers and im still re organizing them so I cant do that again. someone reccomended this ; To boot to the desktop sucessfully, try these follow steps in the WinRE - Command Prompt cd windows\system32\config ren default default.old ren sam sam.old ren security security.old ren software software.old ren system system.old cd regback copy default ..\ copy sam ..\ copy security ..\ copy software ..\ copy system ..\ After this type : EXIT and restart the system. It will boot to the normal mode with the service pack 1 on the Computer. So in future if you plan to install the service pack 2 or any service packs, please do the follow before you install the service packs. * Disable Antivirus / Firewalls * Installing in clean boot state. MSCONFIG . * Make sure all the Driver are up to date. * make sure BIOS is up to date. * Make sure no external device are connected to computer while installing the service packs But when I asked if this affect or delete or change or rename or replace or move any of my data,files,folders or docs I was told it restores the system registry from the backup saved in the Regback folder, but does not change any files on the PC, But what I dont know is what the regback folder is, ive never heard of it and ive not had time to backup my data in the three years ive had my laptop. would be very thankful for some help,