I doubt it's RAM related, with bad RAM you get panics or lock up usually, but it is a serious problem anyway. Seems more corrupt HD and/or file system.
See if you can start in Verbose mode. Hold down Command-V till you see the dos looking screen. If it makes it there where does it stop loading? If it never makes it there chances are you will just need to do a re-install if a disk check gives the all clear, which will still keep his data intact.
Of course do the usual suspects first once you get it into Target Disk Mode. Disk Warrior or Tech Tool Pro if you have it, or at least see what Disk Utility will do.
If DW or DU can't fix it you would need to make sure it's backed up, then wipe and reinstall.
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