HP Pavilion Slimline S3301F (p/n KE553AA). Windows Vista Home Premium 32bit. Windows fails to start. The Safe Modes and Last Known Good Configuration also fail to start. Startup Repair log details say 2 boot-critical files are corrupt, ndis.sys and netio.sys. System Diags. all pass... CPU, RAM, and HDD, and the computer passes POST. Check Disk (chkdsk /r) in UBCD4Win completes. No errors reported. The only recent changes are that I have disassembled and cleaned the computer, applied new thermal paste to CPU, replaced the RAM with OEM-spec sticks from another HP, replaced the CMOS/RTC battery, and reset Time/Date in BIOS. Afterwards, the computer worked perfectly, and completed 3 shutdown and restarts. But when I powered on the computer today...this. The computer did not come with a recovery disk, only a Recovery Partition on the hard drive, and atm, the only OS disks I have are generic XP Home, XP Pro, 7, and Linux (Ubuntu and Fedora). Any help would be greatly appreciated. THANKS much.Best way to fix this is by using a Vista Disc to PERFORM a repair installation if one could be borrowed. If thats not an option, you can boot the system with a Live Linux distro and replace the ndis.sys file and netio.sys file with known good from another system running Windows Vista. Lastly these files can be acquired online, but that would be a last result and would also need the system BOOTED with access to the NTFS partition to copy these files in overtop of the corrupted ones.

*Also to note, problems like this sometimes seem like an endless battle. You replace 2 files that the system is complaining about and you are faced with more problems.

I would suggest that if you can get this system to boot, to CREATE the restore disc set using the utility that should be present on this system, then backup all your data and install clean off of these FRESH recovery discs.Thank you, Dave. Sorry it's taken so long to answer. I did try to use a borrowed Vista install DVD to attempt a repair install, but to work, it needed to be started from inside Windows. Given what you said about possible further issues after replacing the .sys files, I decided to backup the Users' files and do a Factory Restore, then restore the Users' files. Then I created a set of restore disks. So far so good. Thanks again, both for your help, and for your fast response.You should know you can't run a repair install from inside Windows by now...so i don't understand that comment...It is possible to do a repair install of Vista by using the Upgrade option to install Vista over an existing install. But for it to work, it has to be started from inside Windows and it has to be the same version as the one installed. These 3 links explain it better.

http://www.vistax64.com/tutorials/88236-repair-install-vista.html

http://wiki.pcworld.com/index.php/Repairing_/_Reinstalling_Vista_from_Install_DVD

http://vistasupport.mvps.org/repair_a_vista_installation_using_the_upgrade_option_of_the_vista_dvd.htm
I've always ran it from booting to the install CD/DVD's.