Before I rush off and return the Marshall JCM 2000 TSL 122 I just bought from Guitar Center, I just want to know if whats happened is a known problem/easy to fix.

I bought the amp a few hours ago after playing it in store for +- 20 min (after trying numerous other amplifiers) and then brought it home. After 2 hours or so I plugged it in and started playing. 30 minutes later the volume of the amp seemed to drop down to a much lower volume for a few seconds after which the volume then cut completely. Now it doesn't produce any sound - and i've tried both powering it down to standby and then switching it on again, and powering it off and then on again. This is the first tube amp I've owned so I'm still very inexperienced in using them.

When I was playing, the volume and gain on all three channels was around 3-4 and for those familiar with the amp, I had the V.P.R. (Virtual Power Reduction - swaps it down to effective 25w output) switch engaged.
When I turned it off and on again, I did it in the following order: standby switch - 30 seconds -power switch - wait 1 hour - power switch - 2 min - standby switch)

Any advice would be appreciated!
if you say the volume dropped then cut out completely, it sounds like ur valves blew, lol. though make sure its not ur guitar or lead. if ur valves have blown youll just have to buy some new ones and put em in, gives you a chance to get some nice-ass valves tho
How much wood could a woodchuck chuck if a woodchuck could chuck norris

A lot
its a JCM 2000, you should never have bought that in the 1rst place.
My gear:
-Ibanez JS 6000 Custom w/ 11-48 gauge
-Ibanez FGM 400BB w/ 10-46 gauge
-Peavey 6505 2x12 Combo
-MXR Phase 90
-Boss DD-6 Digital Delay
-Morley Wah/Volume Pro Series II
-Boss CS-3 Compression Sustainer
-Gator G-Bus 8
-Xotic BB Preamp
Sounds like you may have a bad tube somewhere in there. Make sure they are all glowing. And they are glowing the same color. Start there.
If you start a reply with: I have never played one but I have heard good things about it! Your opinion is invalid.
You probably should have had it on standby longer. The tubes probably need replacing, seeing how the amp could have sat for a while. If you shocked them that could have blew them if they did, they need to be replaced.
Thanks for all of the responses.

One of the four smaller tubes is not glowing - so I assume this is the one that blew.
Sometimes not all the preamp tubes glow, I think that's normal. However, make sure that all your power tubes are pushed in all the way (LET THEM COOL DOWN FIRST) before jumping to conclusions. My Randall had a loose power tube after being moved back and forth some and it dropped in volume and gain for a little bit. I found the culprit and never had a problem since.
Then there's this band called Slice The Cake...

Bunch of faggots putting random riffs together and calling it "progressive" deathcore.
Stupid name.
Probably picked "for teh lulz"

Mod in UG's Official Gain Whores

All the valves are glowing (some just more faintly then others) and all the valves are seated properly. Right now there is no sound coming out of the amp at all, except for a very faint hum that appears when turning the power initially on.

I assume that if all the valves are glowing, then none of them blew? Does that mean something else is wrong with the amp? Are there any tests that I can do to find out whats wrong?

The problem is that the amp worked when i played it in the shop - and now only after one use its not working at all and I'm not sure how Guitar center will react to that (I've never bought from them before)