sry guys..problem solved...i followed this one which made all the problems>>>>>>3.5. Enable smoother transitions by enabling GPU hardware sync

Enabling this can make a noticeable difference in perceived smoothness of screen transition effects. It may work perfectly or may cause your N900 to hang during certain transitions. (If it hangs, just reboot and disable it)

To enable: (you will need roosh and leafpad installed first)

1. Go to xterminal
2. type root
3. type leafpad /etc/powervr.d/hildon-desktop.ini
4. Change 0 to 1 and save
5. Reboot

i changed it back to zero and it was solved..thanks for ur tym al of you..love u all