PHP文件未在Eclipse PDT的内部浏览器中启动

Eclipse was correctly bringing out the php files in internal browser...but for past one day it just stopped working...When run button was clicked nothing happened...When i started clicking a lot of times,it opens a dialog box with "performing pre-launch check",which fades away quickly and nothing happens...I've checked Window->Web Browser->Internal Web Browser ..checked with php file's properties -> Run/Debug Settings ..nothing seems to work..any suggestions?Eclipse was correctly bringing out the php file