If you chose Win7 fresh install, it's too raw to do much of anything without Microsoft sending updates to it anymore.  Some settings won't work and it's difficult to use the internet.  If you had a fully working Win7, you'd have to run your own security software. On a working PC, download Win10 ISO to a 8GB or bigger blank flash drive formatted to FAT32.  They often come that way anyway.  Download Windows 10 Disc Image (ISO File) Microsoft site  Boot from flash drive on your 745 to load Win10. When a window pops up asking what partition to load Win10 on, delete all previous partitions.  Then click on Next or Install.  Win10 will then automatically create the appropriate partitions and load.  When a window pops up asking for product key, click on link that says "I do not have a product key."  Win10 will then continue to install using the product key that's imbedded in BIOS. 
I replaced the motherboard battery on my OptiPlex 745 and received the Floppy diskette seek failure message. I went into Setup and made sure the boot was set to the SATA hard drive. However, every time that I restart the computer, it gives me the same message. What am I missing or is there something else I should change so the desktop will boot to Windows. Thanks.
Changed Motherboard battery -- Floppy diskette seek failure