However most sources agree on the fact that system diagnostics are only run at startup - so this should not happen in other modes of operation. I googled the issue and found out that three beeps signal a RAM issue. Turn off, turn on, everything normal again. The grey start up screen is interspersed with terminal messages repeatedly sagin '8debugger called: ', three loud beeps. This happend three or four times, every time it boots up as if nothing happened. After a while the screen freezes and I hear three loud beaps (they repeat). I thought some process must have stopped the mac from switching to stand by and kept the processor busy, so no big deal. The MacBook was in standby (as always) but very hot (not usual). I noted the first strange thing a few days ago. My Feb-2011 MacBook Pro hangs with three beeps. WARNING: You should always ensure you have a backup of your data, especially when performing operations such as this! Shutdown both the MBP and iMac and then try rebooting the iMac as normal from its internal drive that now has Snow Leopard installed. 10.6.8) so that you know for sure it’ll boot the iMac fine Reboot the MBP from the iMac drive and then upgrade Snow Leopard to the latest version (i.e. Now install Snow Leopard onto the external drive (i.e. The only ways to get around this is to use another discīoot your iMac into Target Disk Mode by pressing and holding theĬonnect it to your Mid 2009 MBP with a FireWire cable (once connected it’ll be seen by the MBP as an external hard drive) It’s either one that belongs to another Mac or it’s a retail version that’s earlier than 10.6.6.

My guess is that you’re not using the grey disc that shipped with your iMac. In other words, the Snow Leopard disc you’re trying to boot from contains a version of Snow Leopard that is earlier than version 10.6.6 (the earliest your iMac can support).

And Yes, it’s trying to tell you something!Ī looping three beeps in between three seconds during startup is your iMac’s way of telling you that the operating system you’re trying to boot into is incompatible with your Mac hardware.

Macbook pro 3 beeps at startup