i think you are making problems for yourself; i mean :
1- if you have problems with the hardware from day 1 - have i replaced or repired
2-then you have to repair the problem; as said your 2nd DVD may just be bad; fix this problem first
3-update only on a WORKING system (on one with problems, you just run into more problems, as you've found out)
now for resolving this, i suggest to download the ubcd CD :
http://www.ultimatebootcd.com/ and run memtest86+ for at least 1 full pass (may take more than an hour)
then run a disk drive diag from it for the brand you have; then you are sure about the basics.
Once this is ok, we can proceed.