runlevel 5 gdm problem on FC3 fully updated

[Davide Rossetti]

2-3 weeks ago I started experiencing a nasty problem with gdm in 
runlevel 5. display gets blank after X starts then remain blank, but 
DPMS not suspended. ssh-ing in, I can see X running at 100% CPU, 
probably busy looping somewhere. It's a Radeon 9600.
I tried both xorg radeon stock driver and (after experiencing the 
problem) 
kernel-module-fglrx-2.6.11-1.35_FC3-8.14.13.1-0.lvn.4.3+ati-fglrx-8.14.13.1-0.lvn.4.3
with same broken behaviour.

strang thing is, if I set to boot in runlevel 3, login as my user, 
startx then everything seems ok.

related pkgs are:
xorg-6.8.2-1.FC3.34
kernel-2.6.11-1.35_FC3

It's a Dell Precision 340, "old" P4 with 512MB RDRAM

 >cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 1
model name      : Intel(R) Pentium(R) 4 CPU 1.70GHz
stepping        : 2
cpu MHz         : 1695.632
cache size      : 256 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca 
cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
bogomips        : 3350.52

 >lspci
00:00.0 Host bridge: Intel Corp. 82850 850 (Tehama) Chipset Host Bridge 
(MCH) (rev 04)
00:01.0 PCI bridge: Intel Corp. 82850 850 (Tehama) Chipset AGP Bridge 
(rev 04)
00:1e.0 PCI bridge: Intel Corp. 82801 PCI Bridge (rev 04)
00:1f.0 ISA bridge: Intel Corp. 82801BA ISA Bridge (LPC) (rev 04)
00:1f.1 IDE interface: Intel Corp. 82801BA IDE U100 (rev 04)
00:1f.2 USB Controller: Intel Corp. 82801BA/BAM USB (Hub #1) (rev 04)
00:1f.3 SMBus: Intel Corp. 82801BA/BAM SMBus (rev 04)
00:1f.4 USB Controller: Intel Corp. 82801BA/BAM USB (Hub #2) (rev 04)
00:1f.5 Multimedia audio controller: Intel Corp. 82801BA/BAM AC'97 Audio 
(rev 04)
01:00.0 VGA compatible controller: ATI Technologies Inc RV350 AP [Radeon 
9600]
01:00.1 Display controller: ATI Technologies Inc RV350 AP [Radeon 9600] 
(Secondary)
02:09.0 SCSI storage controller: Adaptec AIC-7892A U160/m (rev 02)
02:0c.0 Ethernet controller: 3Com Corporation 3c905C-TX/TX-M [Tornado] 
(rev 78)

 >lsmod
Module                  Size  Used by
nfs                   211785  1
nfsd                  212097  9
exportfs                8641  1 nfsd
lockd                  63593  3 nfs,nfsd
md5                     4161  1
ipv6                  259201  12
parport_pc             28421  1
lp                     12489  0
parport                40201  2 parport_pc,lp
autofs4                26181  18
sunrpc                164485  22 nfs,nfsd,lockd
dm_mod                 59221  0
video                  15813  0
button                  6609  0
battery                 9285  0
ac                      4805  0
uhci_hcd               33497  0
snd_intel8x0           34049  1
snd_ac97_codec         71097  1 snd_intel8x0
snd_pcm_oss            51953  0
snd_mixer_oss          18241  1 snd_pcm_oss
snd_pcm                99657  3 snd_intel8x0,snd_ac97_codec,snd_pcm_oss
snd_timer              33093  1 snd_pcm
snd                    56741  8 
snd_intel8x0,snd_ac97_codec,snd_pcm_oss,snd_mixer_oss,snd_pcm,snd_timer
soundcore              10785  1 snd
snd_page_alloc          9669  2 snd_intel8x0,snd_pcm
3c59x                  44137  0
mii                     4929  1 3c59x
floppy                 64753  0
ext3                  131145  7
jbd                    82905  1 ext3
aic7xxx               175641  8
sd_mod                 19265  10
scsi_mod              140073  2 aic7xxx,sd_mod

 >cat /proc/interrupts
           CPU0
  0:    3741906          XT-PIC  timer
  1:      10848          XT-PIC  i8042
  2:          0          XT-PIC  cascade
  7:          0          XT-PIC  parport0
  8:          1          XT-PIC  rtc
  9:          1          XT-PIC  acpi
 10:     123881          XT-PIC  uhci_hcd, uhci_hcd
 11:     241718          XT-PIC  aic7xxx, Intel 82801BA-ICH2, eth0
 15:      65700          XT-PIC  ide1
NMI:          0
ERR:          0