I know this is common question but i found no suitable answer, so i am asking this again. I installed ubuntu 11.10. I found the bug for ath9k, so set first network boot from BIOS menu. That's worked. I have upgraded to 12.04 yesterday. Now ath9k is creating problem again. First network boot is still enable. ath9k works at start. But failed(connect again and again) after couple of minutes. dmesg show error that it can not weak up in 500us. So i tried #compat-wireless-3.5.1-1. But result is same. I have also added #nohwcrypt=1 option in /etc/modeprob.d/ath9k.conf. Still no luck. I tried #rmmod and then modprobe

sudo modprobe ath9k nohwcrypt=1

dmesg shows me error:

[  400.690086] ath9k: Driver unloaded
[  406.214329] ath9k 0000:06:00.0: enabling device (0000 -> 0002)
[  406.214348] ath9k 0000:06:00.0: PCI INT A -> GSI 17 (level, low) -> IRQ 17
[  406.214368] ath9k 0000:06:00.0: setting latency timer to 64
[  406.428517] ath9k 0000:06:00.0: Failed to initialize device
[  406.428852] ath9k 0000:06:00.0: PCI INT A disabled
[  406.428887] ath9k: probe of 0000:06:00.0 failed with error -5

dmesg error when driver fail:

  355.023521] ath: Chip reset failed
[  355.023524] ath: Unable to reset channel, reset status -22
[  355.023556] ath: Unable to set channel
[  355.088569] ath: Failed to stop TX DMA, queues=0x10f!
[  355.122708] ath: DMA failed to stop in 10 ms AR_CR=0xffffffff AR_DIAG_SW=0xffffffff DMADBG_7=0xffffffff
[  355.122714] ath: Could not stop RX, we could be confusing the DMA engine when we start RX up
[  355.263962] ath: Chip reset failed
[  355.263966] ath: Unable to reset channel (2437 MHz), reset status -22
[  358.996063] ath: Failed to wakeup in 500us
[  364.004182] ath: Failed to wakeup in 500us

I can not install fresh ubuntu because i have lots of application installed.

System :

Acer Aspire 4250
AMD dual core 1.6GHZ
Atheros Communications Inc. AR9485 Wireless Network Adapter (rev 01)

EDITED

Now i am in serious problem. No wifi device is not showing in ifconfig or lshw commands. Only ether-net interface shows. I tried (FN + WIFI) several times to enable the device but nothing helps. Now I have installed fresh ubuntu 12.04. Please help

lshw -c network:

 *-network               
       description: Ethernet interface
       product: 82566DC Gigabit Network Connection
       vendor: Intel Corporation
       physical id: 19
       bus info: pci@0000:00:19.0
       logical name: eth0
       version: 02
       serial: 00:19:d1:7a:8e:f9
       size: 100Mbit/s
       capacity: 1Gbit/s
       width: 32 bits
       clock: 33MHz
       capabilities: pm msi bus_master cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=e1000e driverversion=2.0.0-k duplex=full firmware=1.1-0 ip=192.168.1.114 latency=0 link=yes multicast=yes port=twisted pair speed=100Mbit/s
       resources: irq:45 memory:90300000-9031ffff memory:90324000-90324fff ioport:20c0(size=32)

rfkill command does not show anything but no error.