Make sure the IDE cables are all the way(and not upside down) in and power supply cables are connected in snugg.

That's a pretty old-school machine. It might require a BIOS update to be able to detect such a large drive. (Remember, when that computer was designed hard drives ran about 500megs to 2 gigs in size).

Check with the motherboard manufacturer and see if you can flash your bios.

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Your BIOS does not support drives above 32 GB, possibly even an 8 GB limit (less likely). It likely will not recognize such large drives in their default configuration, even if you use utilities that work for that purpose.

Go to the website of the drive manufacturer and download the drive utility package (MaxBlast for Maxtor, for example). Part of these packages is something usually called EZ-Drive (or similar) which wedges an interrupt to allow large-drive access. The problem is that older BIOSes don't expose this int13h interrupt, so it can't be "hooked".

A Promise or HighPoint (for example) add-in IDE controller would solve this, but would likely cost as much as a used, faster computer...

For this reason, nearly all 40 GB drives can be "strapped" with a jumper to a 32 GB limit (the manufacturer's site has diagrams, if the drive doesn't) so they can be used on those machines that absolutely will not work with larger drives; I've done this and it's better than nothing!