I have a problem when I try to connect my guitar to my computer, via line input. Audacity works well, and I can record what I play on my guitar (selecting from Preferences from where to record to default:line0). But the problem is in Qjackctl :
at first when I click on start it shows this error:

after that when I click on Cancel it gives this error:

This is the log from the messages window:

10:30:37.368 Patchbay deactivated.

10:30:37.416 Statistics reset.

10:30:37.459 ALSA connection change.

10:30:37.497 D-BUS: Service is available (org.jackaudio.service aka jackdbus).

Cannot connect to server socket err = No such file or directory

Cannot connect to server request channel

jack server is not running or cannot be started

10:30:37.512 ALSA connection graph change.

10:30:44.060 D-BUS: JACK server could not be started. Sorry

Cannot connect to server socket err = No such file or directory

Cannot connect to server request channel

jack server is not running or cannot be started

Sat Dec  1 10:30:43 2012: Starting jack server...

Sat Dec  1 10:30:43 2012: JACK server starting in realtime mode with priority 10

Sat Dec  1 10:30:44 2012: control device hw:0

Sat Dec  1 10:30:44 2012: control device hw:0

Sat Dec  1 10:30:44 2012: [1m[31mERROR: Failed to acquire device name : Audio0 error : Method "RequestRelease" with signature "i" on interface "org.freedesktop.ReserveDevice1" doesn't exist

[0m

Sat Dec  1 10:30:44 2012: [1m[31mERROR: Audio device hw:0 cannot be acquired...[0m

Sat Dec  1 10:30:44 2012: [1m[31mERROR: Cannot initialize driver[0m

Sat Dec  1 10:30:44 2012: [1m[31mERROR: JackServer::Open failed with -1[0m

Sat Dec  1 10:30:44 2012: [1m[31mERROR: Failed to open server[0m

Sat Dec  1 10:30:45 2012: Saving settings to "/home/gevorg/.config/jack/conf.xml" ...

10:31:11.438 Could not connect to JACK server as client. - Overall operation failed. - Unable to connect to server. Please check the messages window for more info.

Cannot connect to server socket err = No such file or directory

Cannot connect to server request channel

jack server is not running or cannot be started

Now I can't understand what my problem is.