Are you using IDE or SATA hard drive?

Could have been a mix of both. Bad CMOS chip would could accept a fresh flash, but would not fuction correctly. If he is telling you to install an update, but not the most current, they could have...

With all of that it does sound like BIOS issue then. Sounds like a defective line of boards. Almost like the controller on the board does not see the HDD then suddenly does. That would explain the...

The black screen with cursor means the bios have finished post and is waiting on the HDD to load the ntldr. This is usually an idication a bad MBR, but with you able to shut the system down and then...

Sounds like your HDD is having issues. Like it is having problems spinning up after a cold start. I would recommend a full back up and then replace the drive.