Your line collision algorithm is mistyped and wrong,

1.  if((xpos=x1) && (xpos>y1) && (xpos<y2)){
2.     print("you lose!");
3.     xpos = 40;
4.     speed = 0;
5.   }

first of you used a single = when it should be == secondly you're comparing xpos with y1&y2 when it should be ypos. Thirdly you are checking if xpos equals x1, this can sometimes never be the case, xpos always starts with 40 and x1 is a random number and xpos is always increasing with speed = 2. So what if x1 is a odd number, how can xpos then ever equal x1? Fourthly you are assuming that y1 is smaller than y2, this is also not always the case since both are random numbers.

If you wanna fix this by yourself and learn from it i would suggest stop reading here.

but because i had to write this in order to check if those were the only errors i thought i'd post it anyways so..

spoiler alert
(note: there are more ways of doing this)

1. if((abs(xpos-x1) < speed) && (ypos>min(y1,y2)) && (ypos<max(y1,y2))){
2.    print("you lose!");
3.    xpos = 40;
4.    speed = 0;
5.   }

In this situation when in doubt check the values you're comparing in the condition.  I just added the following at the start of your linecollide() function and the (initial) problem becomes obvious:

println("xpos: " + xpos + "  x1: " + x1);

Your condition checks for equality between xpos and x1 (actually in your code it didn't because you'd done if(xpos = x1) rather than if( xpos == x1) ); but since random() returns a float it's highly unlikely to set x1 to a round number that will match the value of xpos.  You should also consider the fact that xpos is being incremented by 'speed' which is set to 2, so your intended condition would only ever return true if x1 is even...

Assuming that speed will never grow too large one solution is to treat the line as a rectangle wide enough so that the ball will always be within it at the point the line is crossed.  The following condition should work as long as 'offset' is a value greater than speed:

if(xpos > x1 && xpos < (x1 + offset) && ypos < y1 && ypos > y2){
  //...
}

Notice that I also fixed the y position check.  Your code checked the x position against the y position: "(xpos>y1) && (xpos<y2)".

TBH if the ball only ever travels horizontally you could do without the additional xpos check; but I'm assuming that at some point it will travel diagonally ;)

Unfortunately the problems don't quite end there.  Because of the way you generate the y1 and y2 variables the above code won't always successfully generate a hit.  Note that with your current code it's perfectly possible for y2 to be less than y1; thereby reversing the direction of the line at which point the condition won't work...

To fix this just change the way you generate the variables:

float y1 = random(200);
float y2 = y1 + 50 + random(100);

This way y2 is always greater than y1 (and also has a minimum length of 50) ;)

I was too slow!  Though I prefer my solution to the reversed line issue: simple and avoids additional function calls ;)

Wow you see this is why you shouldn't write code in the early morning hours! I feel like such a noob! I'll be posting up the final result soon!