As Endurion pointed out just use the bool in the condition for collision.
if(g_bBlock[4].m_bActive_three==true)
{
if(x>=3.0f && x<=5.0f && y>=3.5f && y<=4.0f)
{
ystep = -ystep;
g_bBlock[4].m_bActive_three=false;
}
}
But trust me, there are much more efficient ways of detecting collision and removing the blocks. The one you are using is probably the easiest but not accurate in many cases.

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