Download older OS to Flash Drive

Most likely the internal hard drive has failed, although there can be other reasons for the blinking folder with question mark.

If you had provided the exact model of the Mac, then we could have provided you with some other options assuming the internal HD is still healthy. Knowing the exact model we could tell if Internet Recovery Mode (Command + Option + R) is an option, or to provide you a range of compatible Mac models for creating a bootable macOS USB installer.

You can get the exact model by entering the system serial number on the check coverage page here (please don't post the serial number on the forum since it is considered personal information):

Check Your Service and Support Coverage - Apple Support

At best I can say you need access to another Mac model (working of course) generally from 2007 to 2015 in order to create a bootable macOS 10.11 El Capitan USB installer using the instructions in the following Apple article:

Create a bootable installer for macOS - Apple Support

A bootable Yosemite installer can technically be made as well although you would need to properly convert the instructions for the El Capitan installer to do so since Apple no longer provides the necessary command in that article.

If you have a Late-2009+ model, then you have a lot of other options for a compatible Mac in order to create a bootable USB installer.

You can only download Yosemite to a Mac that can run it. Then you would have to create a bootable installer.

As far as your issue, see: If your Mac doesn't start up all the way - Apple Support

dialabrain wrote:

You can only download Yosemite to a Mac that can run it.

FYI, technically any computer or OS (even a Windows PC) that can access the Internet can download the full Yosemite installer (as well as El Capitan and Sierra) since they are available directly from Apple in DMG format from outside of the App Store.

Of course this installer in DMG format cannot be used on the broken Mac that is unable to boot into macOS.

Then you would have to create a bootable installer.

This is where using another Mac that is compatible with Yosemite is required since the downloaded Yosemite DMG installer can be transferred to a compatible Mac to make the bootable USB installer.

The point was, downloading Yosemite to a flash drive is pointless without a Mac that can create a bootable installer.