You can try to downgrade again, use a dongle or whatever you have, PS3 you can try to enter the factory mode system, download OFW341 instead of modification, download file also Lv2diag_355, after all you can be right.
You must have a usb pendrive with fat32 format system, For OFW341 file name must PS3UPDAT.PUP, and to Lv2diag_355 use 1 file to downgrade to name Lv2diag.self size 365 KB (374 272 bytes), put the two files on the root of your usb flash without a folder, try only 2 files are in the root of usb pendrive.
Do it now for your PS3 is having problems, turn off the PS3 then insert usb usb pendrive at the far right near the bluray disc, turn on the PS3 wait 3 minutes to stand by.
Her following after you have come out of the factory mode, use files 2 with names of Lv2diag_355 Lv2diag.self with size 201 KB (206 256 bytes), Lv2diag.self enter the root usb pendrive without any other files, do as above, and wait for the PS3 to stand-by.
Having completed all done then your PS3 will return to its normal position, with OFW341 and you can upgrade to 355 or to position the latest CFW. I hope you SUCCEED friend.