lsass.exe system error

okay I have no idea what i did to cause this frustrating issue...but it's happened and now I cannot get passed it. I was trying tune up an older system for a friend that was running extremely slow.

Operating System: Windows XP Service Pack 3

The system has many many programs and personal data on it and was running dog slow like I mentioned. So first thing I do is go into msconfig and remove all third party services and all startup items, then reboot. It reboots fine and is still running pretty slow...so I thought I would add a little memory to boost it a bit. It had 512MB PC133 using shared memory for video. So with only one slot available I added a 256MB PC133 module and tried to boot. Everything seemed to post fine...all the memory tested okay, but when it gets to Windows this error box comes up and in the title bar says "lsass.exe - system error" and in the dialogue box says "an invalid parameter was passed to a service or function" and I cannot seem to get around it in any way. If anyone knows the file that is causing the lsass.exe to not load or has any ideas of what I might try short of a format and re-install I would greatly appreciated it. I seem to always find good solutions at this forum...so this is why I come here with the evil ones. M$ is going to make me go bald...how annoying.