XP Repair/Restore

First time poster on this forum.

I have a Dimension e310 that I purchased new back in 2005.  It's been a great unit until now. 

I cannot boot into windows. Can't boot in SAFE mode (any).  Either way I get an error: "Endpoint format invalid" referring to LSASS.exe. 

Posts I have found refer to a Restore CD, but my computer never came with this CD.  It may have been in the setup instructions to create one, but that didn't happen.

Short of going out and spending more for an operating system than I can for a new PC, any suggestions on how to acquire a restore cd?  Obviously, the unit is out of warranty so unless I pony up the $$, Dell won't talk with me.

THANKS for any assistance.