Startup hanging at first page BIOS

Hi All

Just re-joined, I was a member from very early but seem to have slid through the cracks since.

My system is running superbly but has a strange start-up and BIOS issue I cannot resolve. It started three days ago. Powered on to start my day and stalled on BIOS ..DEL entry screen and I couldn't do a thing. Powered off/ restarted several times with no effect. Left my home office to collect my iPad3 from family room, returned and the desktop in question was up and running at logon screen. Decided to experiment, turned off PC, restarted and waited. Sure enough after about 2 1/2- 3mins it chirped and proceeded, exactly as normal, to logon screen. It does so every time I start-up!

I have revisited BIOS Boot Menu numerous times, set the SSD as Boot Priority, saved exited all those things, nothing has worked. I have run Mem test continually over a twelve hour period no RAM errors found, also ran Disk Checker several times with one error found and repaired. I have excellent, pro version, virus and malware protection, nothing has shown up.

To me, it seems as though start-up is searching for the SSD where the OS is installed and is somehow locked into going to the DVD drive first. Every time I reset priority in BIOS back to SSD drive it automatically reverts back to the DVD drive (P4 in my BIOS) when restarted. My BIOS version is still 13, I'm not fond of fiddling with the BIOS unnecessarily.
However if it is BIOS related I'll deal with that.
The only other symptom I have noticed is that, at shut down, the machine has been closing down considerably slower than normal and has been showing error "Waiting for background files to close down". It shows google drive and email notifier pro also.

I like to run a 'lean machine' with nothing installed that I don't use and want, I love music and have had Asus Xonar Essence XTS installed for quite a while. My PSU is a 1,000W Seasonic (high end), this setup runs very cool and the rails settings all seem correct.

Your advice and assistance would be much appreciated. I can run it as is but it takes about 4 minutes to boot up now and errors get progressively worse if not dealt with early.

Thanks.