|"reputable ebay seller"|
I don't buy on ebay.
As above, check your specs.
Even big name stores can get stuck with bogus ram. There has been for years a market filled with second quality ram and even lower speed ram being re-packaged and re-marked.
"Best Practices", Event viewer, host file, perfmon, antivirus, anti-spyware, Live CD's, backups, are in my top 10