I left the box overnight doing memtest86+ to find:
Since the Ubuntu CD was giving me trouble I succesfuly downloaded, MD5SUM checked, SHA1SUM checked, burned and installed the lastest CD release of the following distros:
Only the mepis install gave me trouble. It complained about a bios bug related to MMConfig. I updated my bios and after that Mepis has been running smooth.
Maybe this bug was giving Debian and Ubuntu's MDSUM a hard time.
Now I have my hand full of linux so I'll stop worrying about it.
Thank you all for your support