OptiPlex 740 - Cannot restore OS

I have a  Dell OptiPlex 740:

Spec AMD AthlonTM 64 X2 Dual Core 5200

2gb DDR2 SDRAM

ATI Radeon HD 2400 Pro 256MB

2 x160 GB SATA HDD Raid 1 ( Mirror)

Vista Business 32 bit

The Raid degraded but the PC continued to work on one disk although rather slowly, rebuilding the raid would not work. I cannot access setup, F2 does not respond. I reconfigured with one HDD, however the recovery disk will not work. I have tried other Vista 32 bit disks but the installation gets so far then nothing. I have successfully installed XP and having done that I re-flashed the BIOS  but F2 will not let me in. I attempted to upgrade to Vista business using the Dell recovery disk by running the installation from within XP , selecting upgrade it copied all files and attempted to run but then died. I am baffled so can anybody help please?