Black Screen, No BIOS, No Windows

[lodders]

My wife,s AMD Phenom II PC is about 6 years old. Very reliable overclocked PC with no problems.
I upgraded to Win 10 a week ago, but had problems with 100% HDD use - purely a Win 10 process - other people on the internet have the same problem with Win 10, PC was fine in Win 7
I had a spare SSD, so I decided to install a new copy of Win 7 on it, then upgrade to win 10

However, my windows 7 install stopped, said a driver was missing. Never seen this before....
I wondered if this was an issue with the really old beige DVD drive, so I borrowed one from my newer PC. Switched off, disconnected old IDE DVD, connected newer SATA DVD, turned on and tried again.
This time no driver issue, but halfway through installation it said a file was corrupted and hung.
Switched off at the mains
Cleaned DVD. Disconnected and reconnected drive. Checked everything else was OK.
Tried again. Same problem. Switched off at mains.
Switched back on - Fans start running, green LED on motherboard, ASUS splash screen, then black screen with no cursor.
Will not boot with original HDD, will not boot with DVD, will not go into bios.
Tried a different (non usb) keyboard
Removed CMOS battery for 10 mins with the mains disconnected.
Splash screen then black screen, and NOTHING else...

Suggestions?

 

[lodders]

Just when you thought my luck couldn't get worse....

I decided to put the spare SSD in my media centre PC instead.

PC has exact same motherboard and processor as the one above - ASUS M4A78LT and AMD Phenom II unlocked to 4 cores.

I disconnected the old HDD, and connected SSD and DVD. Turned it on, put in windows disk during BIOS, and tried to install windows.
However, the monitor went black immediately, and this computer is now bricked just like my other one.

Please can anyone help?
Have you experienced black screen at power on? Do you think it is corrupted BIOS ?
Have you ever had windows install or upgrade cause this kind of problem?