When solving two simultaneous equations..

You know when you times each equation by a number to get x or y the same value and then add/subtract..etc, what if you multiply by a constant and both x and y cancel out?
What does this mean? Does it mean there are no solutions?

Many Thanks!!

Yes, you can't solve the equations because they are not simultaneous.
eg
x + y = 1
2x + 2y = 2
are not simultaneous, and cannot be solved.
the second equation is merely the first equation multiplied by 2.
(strictly speaking, there are an infinite number of solutions)

It either means you've made a mistake in your working, or that you haven't been given enough information to solve the problem.

For example, if I wasn't given any information at all about x and y, I might still make up true equations about them. I'd know that:

2x = x + x
and that
3y = y + y + y

But if I tried to solve these, they would just cancel out, because I haven't actually got any information about this x and y.

But usually, it means you made a mistake in your working. I often find this problem comes up when people start to work with quadratic and other polynomial equations. Are your x's or y's raised to a power?

You need to give us an example of what you mean here. If you multiply the two equations by the SAME constant, you wont have changed anything. Both equations will be effected by the same amount.