[Nexus 5 Q&A, Help & Troubleshooting] mpgrimm2:
Well I did a format of: System, Userdata, & cache ... and an erase on the eMMC partitions (boot & recovery).

C:\Android\WorkingFlashFolder>fastboot format boot
Formatting is not supported for filesystem with type 'emmc'.

C:\Android\WorkingFlashFolder>fastboot format system
Creating filesystem with parameters:
Size: 1073741824
Block size: 4096
Blocks per group: 32768
Inodes per group: 8192
Inode size: 256
Journal blocks: 4096
Label:
Blocks: 262144
Block groups: 8
Reserved block group size: 63
Created filesystem with 11/65536 inodes and 8536/262144 blocks
error: file_write: write: Bad file descriptor
Cannot read image.
erasing 'system'...
OKAY [ 1.320s]
finished. total time: 1.320s

C:\Android\WorkingFlashFolder>fastboot format cache
Creating filesystem with parameters:
Size: 734003200
Block size: 4096
Blocks per group: 32768
Inodes per group: 7472
Inode size: 256
Journal blocks: 2800
Label:
Blocks: 179200
Block groups: 6
Reserved block group size: 47
Created filesystem with 11/44832 inodes and 5813/179200 blocks
error: file_write: write: Bad file descriptor
Cannot read image.
erasing 'cache'...
OKAY [ 0.800s]
finished. total time: 0.800s

C:\Android\WorkingFlashFolder>fastboot format userdata
Creating filesystem with parameters:
Size: 13725835264
Block size: 4096
Blocks per group: 32768
Inodes per group: 8144
Inode size: 256
Journal blocks: 32768
Label:
Blocks: 3351034
Block groups: 103
Reserved block group size: 823
Created filesystem with 11/838832 inodes and 93654/3351034 blocks
error: file_write: write: Bad file descriptor
Cannot read image.
erasing 'userdata'...
OKAY [ 7.970s]
finished. total time: 7.970s

C:\Android\WorkingFlashFolder>fastboot erase boot
erasing 'boot'...
OKAY [ 0.220s]
finished. total time: 0.230s

C:\Android\WorkingFlashFolder>fastboot erase recovery
erasing 'recovery'...
OKAY [ 0.230s]
finished. total time: 0.230s

Followed by a full load of the google factory images for LMY48B. Still hangs at the "Google" logo like something is corrupted in /boot or /aboot somehow? I'm not sure if there is anyway to actually delete/recreate the partitions on the N5 to get it to work. Still open to ideas.

Here is my "getvar" command output if its needed...

C:\Android\WorkingFlashFolder>fastboot getvar all

(bootloader) max-download-size: 0x40000000
(bootloader) version-hardware: rev_11
(bootloader) version-baseband: M8974A-2.0.50.2.26
(bootloader) version-bootloader: HHZ12h
(bootloader) version-cdma: N/A
(bootloader) variant: hammerhead D820(H) 16GB
(bootloader) serialno: EDITED
(bootloader) carrier: None
(bootloader) secure-boot: yes
(bootloader) unlocked: yes
(bootloader) product: hammerhead
(bootloader) partition-size:aboot: 80000
(bootloader) partition-type:aboot: emmc
(bootloader) partition-size:boot: 1600000
(bootloader) partition-type:boot: emmc
(bootloader) partition-size:recovery: 1600000
(bootloader) partition-type:recovery: emmc
(bootloader) partition-size:system: 40000000
(bootloader) partition-type:system: ext4
(bootloader) partition-size:userdata: 3321fa800
(bootloader) partition-type:userdata: ext4
(bootloader) partition-size:cache: 2bc00000
(bootloader) partition-type:cache: ext4
(bootloader) partition-size:persist: 1000000
(bootloader) partition-type:persist: ext4