Tube amp problem

I own Sonic Frontiers Control-1 amp. and just couple of days ago, i started
having a trouble turning the amp on. First day, i checked the fuse and it wasn't blown. When i placed the fuse back and started it, it worked! I turned on and off, couple of times and it worked fine.
Next day, the same thing. That time checking the fuse didn't worked so went through the whole deal of checking the tubes (removing them and trying to turn on), biased. It didn't worked. I placed the cover back and this time it 'fired up'! The only thing, i noticed was the strange static-like noise coming out of the speakers. I checked the speaker wires, but that didn't affect the 'static'. Few minutes later noise disappeared from one speaker than from another. I listened music with no problem for next few hours. Later, i pushed on/off and it worked 'till later that evening where it went silent. Again! Accidently i pushed the amp, and rear two 'feet' went of the stand, and amp turned ON! The 'static' came back but dissipated within the minutes. So each time amp doesn't come on, i gave it a 'slap' and it works!
Your suggestion and/or advice would be greatly appreciated!
Dragan, i expected the help from the Sonic Frontiers, but nothing. Yet!

P.S. Previous day before first trouble occured, i instaled powered Subwoofer via
Eldragon what about the pwr cord? It might have a short or the internal wires from the iec box may be loose. There's a short somewhere if all you have to do is move it. Also check the output jacks and the wires connected to it. Hope this helps.
I agree with south43, there is a short/open some where. You might also check the power switch.
I have an SF phono stage and have had some problems with RF getting into it--causing buzzing and sounding like a lifted ground. The grounding schemes on SF gear has changed due to UL listing and other such requirements. I recommend you call Sonic Frontiers rather than an e-mail. They were very helpful with me. Ultimately I had to shield the phono stage very well--which was a surprise to me since it was already pretty well isolated and I live out in the country. The other possibility is poor connections on the tube pins. I recommend removing them and cleaning the pins thoroughly with De-oxit or some other similar product. You could try a contact enhancer as well. At the same time inspect the sockets and make sure that the pin holders look to be in good shape. Hope this helps and you find the ghost in the machine.
Thanks guys! Troube-shooting in electronics can be a bitch! As Abstract put it: 'Chasing the gosts...'
Dragon, I have to check in agreement with the power cord. This has happened to me a few times. Frustrating as anything you will experience. Please disconnec the power cord from your amp and the wall. Then reinsert. Hopefully, this is all that is wrong. Good Luck!
Thank you all! I think i found the problem. It is the one of the tube sockets solder is going bad! Couple of hours of work this weekend.