You don't use the disk to install Mavericks. You use Recovery HD.
Restart the computer then immediately hold the Command key and the letter R key together until you see the Apple Logo. This will boot to the Recovery HD partition. When it boots you will see a window called Utilities, select the Disk Utility and then select Continue. Then in Disk Utility select Macintosh HD in the left column and then Erase on the right, click on Erase. Quit Disk Utility and Reinstall Mac OS X
I've done that, but for some reason it won't let me reinstall the os x because it says the app store is temporarily unavailable
Are you using WiFi?
Can you connect it direct using Ethernet?
yes, I'll go and do it now
OK let me know
ok its plug in and starting up
ok I'm in utilities
OK erase and install if it fails again we have to try a different way
On the left I've got '1 TB ST310.......' is that what I need to erase? Underneath it has 'untitled 1'
No untitled you can name it Macintosh HD
I've erased it and tried to reinstall and it just does the same thing.
Ok restart and hold Option until you see a list of boot partitions select Network and try to connect to your WiFI
There's only one option - recovery 10.9.5
Under that you don't see a button for Network?
No there's just an arrow
It should look like this
No, I don't have that. Just one picture of the disk and the arrow underneath.
Ok look at the very top of your screen select each one and tell me what you see.
There's nothing at the top - just a grey screen. And it won't let me select anything other than the arrow
Sorry I haven't got a usb stick large enough to hand
8 GB would work
Ok choose Recovery HD again and now look at the top of your screen
there's nothing at the top of the screen
After you boot to Recovery HD when you see the Utilities window again....
Ok, the top gives me the utilities options on the left and then theres a union jack and network symbol on the right
Ok try Network see if you can sign in to your WiFi.
yes I can sign into wifi fine
OK strange then there may be a problem with your Recovery partition that is why I was going to try the USB stick we could erase both partitions.
Try installing again
It just does the same thing. It tries to access the app store and then says 'this item is temporarily unavailable'
OK sorry I am out of ideas let's see if other experts can help
What do I do now?
I assume I don't have to pay for this?
Your question is open to other experts.