You maybe dealing with several problems or actually dealing with the original problem of why the system was given or let go. All this boils down to resolving all issues. If you're using the Dell OEM install discs, be sure you have what the Dell system was build as from day1 to lessen any hic-ups. Further, due to age you can have a worn out mtrbd. and/or dated one that may not accept whatever mish-mash of devices you have to make a system go 100%. The files you're referring to can be a bad read of the install discs, the drive itself or again some device that wasn't part of the install when sold. Get the mnaual and review it as well.
I use HD wipes to totally remove any past installs and restart from scratch, the OS reload. I visit Dell and enter the model s/n and see how it was build or typical for that model#. Then, if possible similar build to try the install. If the Dell discs are not OEM or for that model Dell, be sure to inspect that side of things. Next, assure the mtrbd. itself has no damage as Robert mentioned, "bad caps" as a possible issue. Next, verify the PSU is capable for it to die and not come-ON suggest a weak PSU or mtrbd. Check all that out and get back. Alas, older stuff just bites the dust, prepare to move on.