I tried searching but I couldn't find a specific answer to this issue as the keywords are too general. During startup, my iMac keeps switching to AHT (Apple Hardware Test). There is nothing in AHT. The only other option after AHT completes is Shutdown or restart. After rebooting, it enters the AHT mode again. If I hold down the shift while booting, it boots up fine (in Safe Mode I guess). Any ideas? Should I archive and re-install? Help!!! as i m new to mac. Thanks.