Some time ago a had a problem with a 6100 powermac: it did chime, but refused to startup. This has been solved after installing a new ROM-battery (costing me whopping €18!!!).
I even managed to create a network startup disk, connect it via ethernet to my ibook, and install 7.5.3 via the ibook. Afterwards I updated to 7.5.5, switched from mactcp to open transport. Everything seemed fine, untill.... I turned on Virtual memory: system error 10, crash. On a new startup, the 'welcome to macintosh'-screen shakes like a 'i-won't-let-you-in-since-your-pass-is-wrong-os9/x-login-screen'. Starting up from the bootdisk goes fine. After repeating the entire installation-procedure, the same problem occurred. I changed RAM, so that should not be the problem. Any ideas? Thanks in advance for sharing some precious braincapacity with me!