platform tile collision help

i'm a bit stick with this platform tile thing, and i can't understand why the following produces such weird results.
normally i'm loading in a level from a file, but i've changes this so that it runs as-is.

basically, the little white square doesn't do what it ought to and i wondered if any of you lot could help me make it work properly.

SuperStrict

'make level
Local tileArray:Int[10, 8] ;

For Local i:Int=0To 9
	For Local o:Int=0 To 7
		If i=0 Or i=9
			tileArray[i,o]=1
		Else If o=0 Or o=7
			tileArray[i,o]=1
		Else
			tileArray[i,o]=0
		End If
	Next
Next
tilearray[4,4]=1
tilearray[5,4]=1

'variables
Graphics 640, 480, 0, 60
Local tilesize:Int = 64
Local x:Float = 2 * tileSize, y:Float = 2 * tileSize
Local xVel:Float = 0
Local falling:Int = True
Local gravity:Float = 0.1
Local yVel:Float = 0
Local hit:Int = False

While Not KeyHit(KEY_ESCAPE) 
	For Local i:Int = 0 To 9
		For Local o:Int = 0 To 7
'draw tiles			
			If tileArray[i, o] = 0
				SetColor 0, 100, 255
				DrawRect i * tilesize, o * tilesize, tilesize, tilesize
			Else If tileArray[i, o] = 1
				SetColor 255, 0, 0
				DrawRect i * tilesize, o * tilesize, tilesize, tilesize
			End If
'wall collisions		
'left
			If rectsOverlap(i * tileSize, o * tileSize, tileSize, tileSize, x, y, 1, 19) And tileArray[i, o] = 1
				If x > (i * tileSize) 
					x = (i * tileSize) + 65
				End If
			End If
'right
			If rectsOverlap(i * tileSize, o * tileSize, tileSize, tileSize, x + 20, y, 1, 19) And tileArray[i, o] = 1
				If x + 20 > (i * tileSize) 
					x = (i * tileSize) - 22
				End If
			End If
'bott
			If rectsOverlap(i * tileSize, o * tileSize, tileSize, tileSize, x + 20, y + 20, 1, 1) And tileArray[i, o] = 1
				If falling = True
					If y + 20 > o
						falling = False
						yVel = 0
						y = (o * tileSize) - 20
					End If
				End If
			End If
'top
			 If rectsOverlap(i * tileSize, o * tileSize, tileSize, tileSize, x, y, 1, 1) And tileArray[i, o] = 1
				If falling = True
					If y > o
						hit = True
						yVel = -yVel
						y = (o * tileSize) + 65
					End If
				End If 
			End If
'collide only with tile 0
			If hit = False
				If rectsOverlap(i * tileSize, o * tileSize, tileSize, tileSize, x, y, 20, 20) And tileArray[i, o] = 0
					falling = True
				End If
			End If
		Next
	Next
	hit = False
	
'move player	
	If KeyDown(KEY_LEFT) x:-2
	If KeyDown(KEY_RIGHT) x:+2
	If KeyHit(KEY_UP) And falling = False
		yVel:-6
		falling = True
	End If
		
	If falling = True
		yVel:+gravity
	Else
		yVel = 0
	End If
	y:+yVel
	
	SetColor 255, 255, 255
	DrawRect x, y, 20, 20
	
	Flip;Cls
Wend

Function rectsOverlap:Int(x1:Float, y1:Float, w1:Float, h1:Float, x2:Float, y2:Float,  ..
					  w2:Float,h2:Float)
	If x1 > (x2 + w2) Or (x1 + w1) < x2 Then Return False
	If y1 > (y2 + h2) Or (y1 + h1) < y2 Then Return False
	Return True 
End Function

cheers
charlie