Test the RAM & the hard drive.
test the RAM with this: Memtest86.com - Memory Diagnostic
test the hard drive with drive maker's diagnostic software (the DOS version). Links are here: Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.
Both downloads will be an ISO CD-image file from which you can make a bootable CD on a working computer. Boot your faulty computer from those CDs separately for each test.
test the RAM with this: Memtest86.com - Memory Diagnostic
test the hard drive with drive maker's diagnostic software (the DOS version). Links are here: Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.
Both downloads will be an ISO CD-image file from which you can make a bootable CD on a working computer. Boot your faulty computer from those CDs separately for each test.