I'm still using my Dell Dimension 8300; with Win7Pro32bit and four 6TB hard drives.
Years ago I found that only when cold booting the PC I often needed to Ctrl-Alt-Del at the BIOS (so I'm in the habit of pressing F12 after the power button so I can Ctrl-Alt-Del at the boot menu).
In a thread here I can't find, I was advised to change the CMOS battery (which I now do more often than I need to); this didn't help.
At some point I stumbled upon another trick, while trying to solve a new issue (which may have coincided with my use of very large HDDs) with newly added SATA HDDs being recognized by the BIOS but not Win7.
I'm not talking about Alt-E, Alt-F ("IDE Drive Detection") in BIOS setup; I've always known that I need to do that every time I add/remove an internal SATA HDD.
My newest trick is that I often find a simple "IDE Drive Detection" is not enough. Unless I do it first WITH ALL SATA CONNECTORS DISCONNECTED FROM DRIVES. And only then do it again with all SATA connectors connected. Only thus can all my internal HDDs (on SATA connectors directly, and from PCI SATA cards) be seen by Win7.
Usually it's when I add a 10-year old HDD to the existing drives (this drive passes both CHKDSK and HDD diagnostics).