What operating system disk are you using ?
The error message looks like one from the MSDOS cd rom driver
Googling suggests similar errors with Windows 98
I would expect a Dell Optiplex 745 to run Windows XP
A Dell XP recovery CD would have no problem installing
What does the Windows COA sticker on the PC say the OS is ?
Also there are two VGA outputs one on the Nvidia Quadro FX and another on the motherboard which has an Intel Integrated Graphics chip
Which one is used on startup is usually a BIOS option.
You can leave the Nvidia Quadro FX card out until Windows is installed
If you want to install Vista or 7 you need to find out if a Sound chipset driver is available from Dell for this model