How to jump with gravity always pulling down

I have created a program that makes my blob fall from the sky and when it hits the block sprite it stops from falling. If I walk off of it I fall again (When I fall past a certain spot I come back from the top just to make it easier to work with for now). Anyways, but one of my problems here is my collision isn't working properly, I am going about half way into the object before I stop. So how can I fix that?

My next problem is jumping with the gravity being consistent, I press space but I only go up a very small amount and I am back down. I can I fix this so I jump say about 200 pixels high and then gravity kicks back in and pulls me down again? I want to fix this problem with the gravity not being set to 0 all the time. (If that is possible).

Here is my code(C++),

//set sprites properties
	blob.x = 150;
	blob.y = 0;
	blob.width = 64;
	blob.height = 64;
	blob.speed.x = 0;
	blob.speed.y = 0;
	blob.accel.x = 2;
	blob.accel.y = 10;
	blob.direct.x = 0;
	blob.direct.y = 0;
	blob.gravity = 2;
	blob.inAir = true;
 
	land.x = 100;
	land.y = SCREEN_HEIGHT - 192;
	land.width = 800;
	land.height = 64;
 
	block.x = 400;
	block.y = land.y - 64;
	block.width = 64;
	block.height = 64;
 
//collision function
int Collision(SPRITE sprite1, SPRITE sprite2)
{
	RECT rect1;
    rect1.left = sprite1.x + 1;
    rect1.top = sprite1.y + 1;
    rect1.right = sprite1.x + sprite1.width - 1;
    rect1.bottom = sprite1.y + sprite1.height - 1;
 
    RECT rect2;
    rect2.left = sprite2.x + 1;
    rect2.top = sprite2.y + 1;
    rect2.right = sprite2.x + sprite2.width - 1;
    rect2.bottom = sprite2.y + sprite2.height - 1;
 
	RECT dest;
	return IntersectRect(&dest, &rect1, &rect2);
}
 
//jump function
void jump()
{
	if(!blob.inAir) //if inAir = false
	{
		blob.inAir = true;
		blob.direct.y = -1;
		blob.speed.y += blob.accel.y;
	}
 
}
 
//movement function
void movement()
{
	if(Key_Down(DIK_LEFT))
	{
		blob.speed.x += blob.accel.x;
		blob.direct.x = -1;
		if(blob.speed.x > 8) //allow only a certain speed
			blob.speed.x = 8;
	}
	else if(Key_Down(DIK_RIGHT))
	{
		blob.speed.x += blob.accel.x;
		blob.direct.x = 1;
		if(blob.speed.x > 8) //allows only a certain speed
			blob.speed.x = 8;
	}
	else
		blob.speed.x = 0; //if I am not pressing button my speed is 0
 
	if(Key_Down(DIK_SPACE))
	{
		jump(); //call to jump function
	}
}
//check collision function
void checkCollision()
{
	if(Collision(blob, land))
	{
		blob.speed.y = 0;
		blob.direct.y = 0;
		blob.inAir = false;
	}
	else if(!Collision(blob, land))
	{
		blob.speed.y += blob.gravity;
		blob.direct.y = 1;
		blob.inAir = true;
	}
}
 
//update function
void update()
{
	blob.x += blob.speed.x * blob.direct.x;
	blob.y += blob.speed.y * blob.direct.y;
 
	if(blob.inAir == true)
	{
		blob.direct.y = 1;
		if(blob.speed.y > 30)
			blob.speed.y = 30;
	}
 
	if(blob.y >= SCREEN_HEIGHT + 64)
	{
		blob.y = -64;
	}
}

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