Ok,I have a guitar with a single coil and two hambuckers,zoom g1xn and a cube 20 amp(I sometimes use a 720w sony amp),both of them are without distortion.So,when I play a note or anything for a moment,it doesn't stay for long.I mean,when other guitarist plays their one,it sounds like-"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa' and continues for a lot of time but mine one stays for 4-5 seconds and then shreds rapidly.I want it to continue its sound.
P.S-I play rock and metal genre....Thank you....
Does your amp have a built in noise gate? if it does, turn it off.
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate
Are you using any vibrato at all?

4-5 secs is completely normal in regular mid range guitars in my experience just letting a note ring out without any vibrato or FX at bedroom volumes.
Spin 'round carousel when your horse isn't screwed in.

My band:
Fractured Instinct
(For fans of Death/Groove/Prog Metal)

Ibanez RGA42E
Ibanez S420
LTD H-301
Ibanez RG520
Peavey Predator USA
Douglas Grendel 725
Line 6 Pod HD500X
Feedback helps sustain. Try sustaining a note and facing the speaker.
Epiphone Les Paul Standard
Godin Velocity
Peavey Vypyr 15 Watt
AMT WH1 Japanese Girl Wah
Marshall BB-2 Boost/OD
Joyo JF-07 Classic Flanger
Joyo JF-37 Analog Chorus
Actually I realised that my tone mode was off,so it was not continuing for a lot of time,now it is working,thanks all for your suggestions...