Have you tried a different CD drive?

Parts tested by memtest86+ are Processor, Northbridge (memory controller),
and the memory itself.

If the voltage supply feeding the Northbridge is lower than normal,
the Northbridge can start making errors. The same is true of the
voltage supply feeding the DIMMs. These would be examples of
motherboard faults, requiring an (expensive) motherboard
replacement.

Try testing with only one DIMM or SODIMM. If the machine has
two slots, test the slots individually, and see if one slot
works better than the other.

Even if there are other problems that are preventing Windows
from being installed (such as a scratched installer CD),
you should still be able to pass memtest86+ with flying
colors. Memtest86+ is relatively easy to pass, and
the memory would have to be in bad shape, for errors to
show up. (For example, even if memtest86+ reports no errors,
you can still have problems installing Windows. To test
for that possibility, you need to use a Linux LiveCD and
get a copy of the Linux version of Prime95 from mersenne.org.
Prime95 is a better test that the computer works well. For
me, if I can run Prime95 for four hours, with no errors
reported, then the memory is good.)

   Paul