Area-51 R7, buy a replacement motherboard

GIve your local Dell office a call and ask for "spare parts".  In the US, the phone number is 

1-800-357-3355

These don't seem to be available through the usual channels - and they're proprietary enough that an aftermarket board isn't going to swap into the existing case.

There are plenty of Area 51 motherboards on eBay.com, but that are advertised by their Dell part number.

What is the Dell part number printed on your motherboard ? 

These R7 systems use AMD Threadripper CPUs -- they're not widely available.  If you have a link for one, please post -- I looked all over EBay and from other suppliers, and have seen none available.

Searching by the Area-51 R7 single motherboard part number 5J3W0 might yield results?

I search everywhere ask everywhere for this motherboard 5J3W0 but ni one seems to have it i contacted itprice they dont have it i dont know what to do

What CPU do you have, first or second gen 1900 or 2900 series?

The R6 and R7 use the same chipset X399 and socket TR4, just no BIOS update for gen 2 threadripper.  So if you had a 1900 series you may be able to use an R6 motherboard, which are sold on ebay. 

Re: The motherboard fried so i don't know what to do. 

these days bricked board can be potential revived by flashing the bios chip using a bios programmer.  It has a learning curve.  Search for ch341a programmer for example.