Confirming RAM memory as a cause

Hello,

My aging Toshiba laptop had 512megs of RAM, so I decided to put in 1 gig (two 512meg cards) to max it out
1) put in one new 512 along with an old 256: booted and ran fine and faster
2) Picked up two more used 512's to replace the remaining 256. Put in #2 - fan ran, no apparent disk spin, and no indication of boot proceeding.
3) Put in stick #3 in place of #2, thinking stick was bad - same result as 2
4) Pulled out the new 512 and went back to the old 256 along with the original new 512, as at (1), and now the computer booted and ran fine again, as it did then.

Diagnosis: bad bad rams... dams. I wish there was a way to test them off the computer.

5) Found my old windows 1.0 rubber eraser and cleaned the contacts on the new 512's (cleaned the eraser, and went carefully along the contacts insert direction so as not to leave debris between the contacts)
5.a) new 512 #2 now works! the computer boots.
5.b) new 512 #3 inserted and it works also.

Recommendation: if inserting used ram, find the eraser and clean contacts first! It may save a few loops.

Thanks for the eraser cleaning idea. -dr