i just bought a brand new american standard strat and i use a mg100hdfx head and 412a cabinet and when i played the clean channel it wasnt loud enough no matter how high i put amps volume. i plugged in my other guitar, a ltd viper 50, playing with the same settings it was way louder. it was a huge difference. i cant make the strat as loud, the volume is so low.i took it back to guitar center where i bought it and there was nothing wrong with it. can comeone please help me, i dont know whats wrong, the amp or the guitar.
You bought an American Strat, and then an MG?

People here will flame you for the MG. Really, it's not a great amp and the problem is probably some electrical issue due to poor quality control by Marshall (or Park, who makes that model before Marshall rebrands them).
Sorry, I didn't realise that you'd tried it with another guitar, not another amp. Lazy reading on my part.

1) Try turning up the volume like everyone else is suggesting.

2) If that doesn't work, experiment with stuff and give us more details.

3) If you can get a refund for the MG, do it. Look into a higher quality amp, even if it's SS. The 100 watt version is just a big practice amp that looks cool, but sounds kind of bad and has a high failure rate.
the volume on the guitar is all the way up. but it dosent make sense because theres a huge difference when i play the two guitars. could it still be the amp?
what kind of pups does the viper have? If it has real EMGs then that would explain the problem since single coils have a lot less output than active pups.
I don't give a shit if you listen to me or not
You said you took it to GC where there was nothing wrong with it. What combination of things did you try that it worked with? We need more details.
the viper has humbuckers, yea they told me it could be the pickups. at guitar center they compared the strat to the other ones and plugged it in to some different amps including the MG
If it worked fine with other amps it may just be your MG.
I don't give a shit if you listen to me or not
well yea i thought it was just my MG but why would it still sound way louder when i play my viper on it?
Did you take your MG to GC too?

I think what you need to do is take all your gear and try these combos:

your strat -> your MG
your strat -> another MG
another strat -> your MG
another strat -> another MG

See what the results are.
There's no way for us to know, do what the one guy said and you'll have your answer.
I don't give a shit if you listen to me or not
I don't know, "quite" is subjective. We're not there to hear it and mess with it, so it's hard to say. It would be best to swap the MG for a better amp regardless, but it could be something wrong with it too. Or your pickups just might need to be raised or something. Maybe there's some bad soldering. Something simple that's an easy fix. If it is the MG, it would cost more to fix than it would to get a new amp because problems with SS amps are hard to diagnose. And MGs tend to break often. But there's no reason why one particular amp should be quite with one particular guitar.