What do you do...

[Thermodyne]

The majority of the data is still there. You just need to boot from a diskette and work it from the command line. Depending on the file that was lost, sometimes it can just be replaced after booting the system.

One particular brand of chip set has become a problem of late. The data problems are caused by aggressive DDR timings. You need to correct the cause of the problem, or you will get to revisit the problem at a later date.