fedora 20 in virtualbox/VMWare workstation

[Rafnews]

Hi,

i'm posting now this message as i didn't get any support/suggestion in 
fedora newsgroup till now.

Till now, my fedora 19 was installed as guest in VMware workstation and 
worked great.
when i upgraded it to fedora 20, everything is ok (text console, grub 
etc..) till X start.
it doesn't matter if it starts automatically or manually(with startx) 
everytime it ends with a black/blank screen.
vmware tools are installed but nothing changed.

i imported the same virtual machine (fedora 19) into VirtualBox and it 
works also great !
but once again after removing vmware tools from this version and 
upgrading it to fedora 20, i have the same issue...
when X starts it ends with a blank/black screen.

in both case, i can return to text console using CTRL+ALT+F5.
so it seems that the problem is only with X window system.

Any idea what should i do or what should i check ?
thx.

A.