Q: My Mac freezes after I moved it.

See if you can select a startup disk.

Shut down the Mac.

Wait ten seconds then restart while holding down the Option key. That should launch the Startup Manager window where you can select the startup disk then click Restart.

Since you just moved the iMac (and assuming nothing else changed on the iMac), one thing different is the way (and where) it is connected to power.  Check how it is now connected to power.  If it's plugged into a power strip (surge suppressor), and there are many other peripherals (like that Xserve, a collection of power adapters, a printer, etc.) connected to the same power strip, the iMac may not be drawing enough power to operate reliably.  Try connecting the iMac to a separate wall outlet, or to another power strip with fewer items (and not the Xserve), to see if that makes a difference.

Another possibility, since this is an older iMac, is the PRAM battery (if it's never been changed).  It may have been weak but still (barely) working at the old location.  But when you unplugged it (for moving), the PRAM battery, which provides power to hold some of the Mac's key settings when disconnected from power, drained completely.  A dead (or weak) PRAM battery can cause startup issues, like what you describe.  You can try doing the Reset PRAM ("NVRAM") procedure to see if it makes a difference, and at least gets the iMac to complete startup.

How to Reset NVRAM on your Mac - Apple Support

Oh, sorry.  That would be a "Power Mac G5," so I thought I saw "iMac" (and not just "Mac").  I have a Power Mac G5 myself, serving a useful purpose. 

And yes, my previous reply is applicable, since it probably draws even more power and its PRAM battery would also be getting quite old (if it has never been changed).  And the Reset NVRAM procedure is a basic troubleshooting "thing to try" that is applicable to all Mac models.

FYI - If you need to replace the PRAM battery, most Power Mac G5 models use one like this

https://eshop.macsales.com/item/NewerTech/BAA36VPRAM/

The last ("Late 2005") Power Mac G5 uses one like this

https://eshop.macsales.com/item/NewerTech/CR2032/

Actually, since there's some confusion with your Mac's name, and there is no model that is called "Mac G5"...  It's not a "Mac Pro," correct?  A G5 is the older PowerPC processor, used in Power Mac.  A Mac Pro uses the Intel Xeon processor.

Natalie Raichl wrote:

 

Wow!  You were right. When I isolated the Mac from everything else, it powered right up!  All working now.  Thank you.

 

Quick question: where is the PRAM battery located? Might as well change it out.

Power Mac G5 PRAM Battery Replacement - iFixit

https://www.ifixit.com/Guide/Power+Mac+G5+PRAM+Battery+Replacement/1951

NewerTech 3.6V Lithium PRAM Battery For Select Apple Desktop Systems

https://eshop.macsales.com/item/NewerTech/BAA36VPRAM/

It wasn't 100% clear which Mac model you have.  Select About This Mac from the Apple menu.  Then click More Info, which opens System Profiler with your Mac's profile.  With Hardware selected in the sidebar, what does it say to the right for Machine Name and Machine Model?

NOTE:  The last Power Mac G5 model uses a different PRAM battery compared to earlier Power Mac G5 models.

That's one of the earlier Power Mac G5 models, so it uses the cylindrical battery type, not the one that looks like a coin.  Seems to be easily accessible, on the motherboard next to the slots (assuming you don't have PCI cards in the slots).  Be sure to note the battery's orientation before removing it.

But if the actual problem was how the Power Mac was connected to power at the new location, and that's been resolved, the battery is probably fine if the Mac is (and has been) almost always plugged in.  I don't recall ever replacing the PRAM battery in my Power Mac G5.

Thanks for pinning it down...

The iFixit link has pretty pictures showing where and how

I was assuming that the OP would refine search to their Mac model after landing on the pages - there I go assuming again