Sounds like you had a trashed disk or something... You normally don't need to boot from USB or external device except in extreme circumstances ( remember having to do it exactly once, and that was a net boot).
The SOL note for it is
http://support.f5.com/kb/en-us/solutions/public/10000/800/sol10819.html?sr=22278002
Normally when installing v10 and above it's as easy as running the image2disk utility with the appropriate parameters. THen watch and wait... The exact sequence is normally described in the release notes for the version you're installing.
H