Flashing folder with a ? mark in it. What does it mean??

It means the Mac cannot locate a bootable volume probably due to a drive failure unless you erased the drive especially on an older Mac. I hope you have a backup. If you don't have a backup and the drive is physically failing, then anything you attempt will most likely make the failure worse where even a professional data recovery service cannot recover the data. If the drive is not physically failing, then here is an Apple article explaining the issue with steps on how to resolve it:

If your Mac starts up to a question mark - Apple Support

If your Mac uses a hard drive and is a model from 2007 to 2012, then I can provide instructions to check the health of the hard drive using a bootable Linux USB stick if you are interested.

wehu wrote:

I have tried to reboot in safe mode using press command R while switching on. It proceeds as far as

Entering netwofk and password, but fails to progress . After several minutes the message " contact apple support appears " with error code 2002u

Help would be greatly appreciated.

regards.

Bill.

First Command + R boots into Recovery Mode which does require a reliable connection to the Internet. The large negative error numbers mean there is some sort of network issue. Try connecting the Mac directly to the router using an Ethernet cable and any necessary adapter for a faster more reliable connection that also avoids hard to troubleshoot WiFi issues.

You can also try a PRAM Reset in case the Mac is stuck booting to a bad link (if you have an Intel Mac).

FYI, Safe Mode is a method of booting macOS with third party drivers and Login Items disabled in case there is a software issue causing a boot issue, but this won't help if the Mac boots to a blinking folder with a question mark. Here is an Apple article with information about Safe Mode:

https://support.apple.com/HT201262

I have tried to reboot in safe mode using press command R while switching on. It proceeds as far as

Entering netwofk and password, but fails to progress . After several minutes the message " contact apple support appears " with error code 2002u

Help would be greatly appreciated.

regards.

Bill.