HP Probook 4540s no sound from Headphones or external speakers

Hi everyone,
I bought a HP Probook 4540s-Intel i5-3210 2.50 GHz, 6BG RAM, AMD Radeon HD 7650M 2GB DDR3 and an internal Intel HD Graphics 4000.Currently using Windows 7 Ultimate 32bit.The problem is that I installed the sound drivers from the HP site (IDT High-Definition aoudio CODEC) but the sound is only comming from the laptop speakers.Nothing happens when I plug in  headphones or external speakers.Please help me because I have to use at least my headphones at work.