There are Fujitsu downloads still available. I guess this is the original source, needed BIOS update files for Esprimo P556/2:
https://support.ts.fujitsu.com/IndexDownload.asp?SoftwareGuid=674C6898-055E-43F4-8D1F-8F288B82224E
BTW...hundreds of bricked PCs also here in Slovenia. Beside P556, some All-in-One X models are affected, too. Will see, if this BIOS flash helps.