Startup crash

[Abdul]

I added a NVidia 9800 GT graphics card to my system and it stopped booting...though the message doesn't seem to be related.

login: lock order reversal
1st 0xfffffe0006ff3848 filedesc structure (filedesc structure) @ /pcbsd-build90/fbsd-source/9.0/sys/kern/kern_descrip.c:1193
2nd 0xfffffe008b9b5278 zfs (zfs) @ /pcbsd-build90/fbsd-source/9.0/sys/kern/vfs_subr.c:4212
KDB: stack backtrace:
db_trace_self_wrapper() at db_trace_self_wrapper+0x2a
kdb_backtrace() at kdb_backtrace+0x37
_witness_debugger() at _witness_debugger+0x2e
witness_checkorder() at witness_checkorder+0x807
__lockmgr_args() at __lockmgr_args+0xdc6
vop_stdlock() at ..+0x39
VOP_LOCK1_APV() at ..+0x9b
_vn_lock() at ..+0x47
knlist_remove_kq() at ..+0x67
knote_fdclose() at ..+0x177
kern_close() at ..+0xe9
syscallenter() at ..+0x1aa
syscall() at ..0x4c
Xfast_syscall() at ..+0xdd
--- syscall (6,FreeBSD ELF64, close), rip=0x8015972bc, rsp = 0x7fffffffd868, rbp=0x801807ad0

The issue is reproducible.

[drulavigne]

Is the onboard video still enabled in the BIOS? If so, try disabling it to see if that fixes the issue.

[Abdul]

Disabled, the problem is still here.

[Abdul]

I decided to try to reinstall the OS.
Sadly, installer doesn't boot but crashes with the same error, :/

[Abdul]

I started the installer in VESA mode. It run OK, except for one minor glitch (will post a picture later). The system works OK, except that when I got to display settings in the control panel, I get the crash again and system restarts.

Again, it's reproducible.

ADDED: Sorry, it's not fine.
There is a crash during each startup, but then the OS immediately goes to detect video device (or something like that) and I get Display Settings window, the same as on the first startup.
ADDED:
Correction:
The Display Settings doesn't show up at every startup. It kept showing up as long as I kept crashing my system instead of shutting it down properly. Now it seems gone.