Dear colleagues, I have next problem with different

Dear colleagues, I have next problem with different ACER ASPIRE 5104WLMI.
The problem was that USB (on all ports) was working only as USB 1.1 and often didn`t recognize USB devices attached to it.

I found IXP460 was defective with brown spot on it. I take him of, cleaned footers, checked them and soldered brend new IXP460 with leaded balls.
The result was no reaction from power button. Only green light starts for less then second and then nothing.
I tried to heat chip again, if I didn`t heat him enough. Nothing changed.
I take of this chip and placed another brand new. Maybe first one was broken also. Result is same. I tried even third chip with same resut.
On Power button I measure 17-19V as it sould be on working mobo.
I must say that I used only low temperatures from up and low heater, just enough for solder to melt properly. No footers were broken during procedure.
I see no demaged smd components near heating place.
I changed about 50 chips of that kind using same procedure end precaution measures until now and never had this effect.
What could went wrong?