Please help.............help

i try to [font=Arial][size=2]move an object around on the screen
[/size][/font][font=Arial][size=2]by using the arrow keys

and i did it but the problem is when i click two arrow keys
simultaneous the object moves only by on direction
if i clicked by example the up key and left key the object moves only to up or to the left
and i need to move the object inclined

[color=Red]**please help

onClipEvent (keyDown) {
aa = Key.getCode();
if (aa == 37) {
_root.aa = “left”;
setProperty (this, _x, getProperty(this, _x)-4);
}
if (aa == 38) {
_root.aa = “up”;
setProperty (this, _y, getProperty(this, _y)-4);
}
if (aa == 39) {
_root.aa = “right”;
setProperty (this, _x, getProperty(this, _x)+4);
}
if (aa == 40) {
_root.aa = “down”;
setProperty (this, _y, getProperty(this, _y)+4);
}
}

** [/color][/size][/font]