it would seem that when your hard drive is full, "Reboot to dash", just returns back to the bios menu again, this is due to the available memory being zero.
when in ms dash, full hard drive boots to the hard drive manager to let you delete savegames/etc, however with modchip enabled, it gets "stuck" on the bios screen, preventing you from booting other dashboards with the "reboot to dash" option,
Best resolve for this, is to boot to bios menu, ftp into the xbox and manually delete certain files you do not need, thus resolving the issue.
when in ms dash, full hard drive boots to the hard drive manager to let you delete savegames/etc, however with modchip enabled, it gets "stuck" on the bios screen, preventing you from booting other dashboards with the "reboot to dash" option,
Best resolve for this, is to boot to bios menu, ftp into the xbox and manually delete certain files you do not need, thus resolving the issue.