Hi, I first installed YDL 5.0.
then found out that the network did not work.
so I formatted the ps3.
I see two possibilities:
1) you have formatted the disk and wiped out both Yellow Dog and PS3 GameOS. You will have to re-install PS3 GameOS.
2) You formatted only the Yellow Dog partition. PS3 GameOS is still there. But, when you installed Yellow Dog, it wrote it's bootloader to the MBR (master boot record) of the hard drive. Now PS3 will not boot because the MBR needs to be restored for PS3.
I don't know anything about the PS3. So I can only suggest that you re-install PS3 GameOS.