|I know this is an old thread but hopefully it can help someone ...|
My sisters computer was suffering from the same issue, 1 long beep that lasted 6 seconds then nothing for a few seconds then another 6 second beep. There was also no video display whilest this was happening.
I removed the memory module from the memory slot it was in and moved it to the next slot, ensured it was properly seated then reboot. The operating system loaded without issue.