Dell motherboards require Dell Cases with Dell front panel boards and cables.
Raw motherboards going into generic cases is not supported ever.
790 is from 2009 and end of life. Not likely it has a warranty from Dell.
Front panel cables and boards are model specific. You did not say which Size you have.
The 7020 is the replacement which is several generations newer.
This is a user forum not interaction with Dell support.
There are several SIZES of 790
Front panel is different on USFF vs SFF vs DT vs MT
Mini Tower (MT) pictured below.
Because these models are over 5 years old I'm not understanding any warranty for an END OF LIFE system.
The os is XP /VISTA / 7 ?
Bios version A00 - A20 ? Which version?
If it has a warranty then you should contact warranty support.
Regulatory Model: D01U (USFF)
Regulatory Model: D03S (SFF)
Regulatory Model: D05D (Desktop)
Regulatory Model: D09M (Mini Tower)