New to linux
Do you mean that this machine starts up and boot cleanly from cold, but fails when told to perform a reboot from an already booted system?
After the reboot error now every time I boot it fails
usually that error means something is wrong with your file system.
To fix that you will need to boot from a Fedora live USB stick.
Do you have one?
I’ll try that once I get a pendrive !
In the USB stick should I have the same version of fedora?
It shouldn’t matter - doesn’t actually need to be running Fedora. You’ll be using it to run a disk check on the disks in your machine, so as long as it supports whatever formatting system you have on your main machine, it’ll be fine.
Got it 
Gnome Disks provides drive “health” checks. You can also try mounting the partitions. If that works, journalctl can be used to view the journal on the system drive. You will want to read at least https://docs.fedoraproject.org/en-US/quick-docs/viewing-logs/ and maybe some of the other introductory tutorials.
Not in this case, as those are only the devices which are present on your live USB session. df only shows mounted devices and as such, you aren’t seeing your disks which are in your laptop or PC and which your main Linux system uses, as they are not mounted.
Issue a lsblk -f and you’ll see from the device sizes that you get to see your normal drives and which are all probably much larger than 4 GB.
It’s those much larger drives you want to be checking with the appropriate fsck program for that filesystem type.