Well, you can resell it "unopened" and check offers, that's up to you.
if you plan to use it, then I would definitely get a new CMOS battery as required before any use, 5-6 yrs. it maybe too old or weak. Next, open the box and set it up and run it. Your packing slip should offer what it has and compare to today's offering. Use the S/N# or model# and check HP support fro specs on your PC.
As for AV and protection plan, those are moot points now, clearly "outdated". About the only thing I would keep is the monitor or sell as part of the package, "unopened" maybe for $200 for all or check offers. Go online and see what a PC like yours is going for.
I bought an HP Pavilion Media Center m7590n PC desktop in 2006 w/19" widescreen monitor, battery backup system, HP printer,wireless mouse and keyboard etc...It's all been sitting in its original packaging ever since unopened for 5 or 6 years! I realize the technology has improved but its pretty nice and loaded with features.
What special steps and procedures should I take when setting it up and starting it up?
Is it worth the trouble even or should I just sell it, I paid 1150.00 dollars for all the stuff listed and some AV and a 3 yr prot plan?