Windows 7: After windows loading screen problem!!

When i turn on my computer(an hp pavalion a1720n),it seems fine, i bought it refurbished recently from a computer store in mt. Vernon. After opening up the case to try to install a floppy disk drive,realizing it didnt fit the plugs, and giving up, i turned on my computer a few days later to see it load at the windows logo, after that finished, it became stuck at the small waiting period between the windows screen and the login screen, i can move my mouse, but i have to turn off the computer via the power button. All safe modes dont work. Pressing f11 at the boot menu doesnt work. And im stuck at that. Please help!

As you open the case, check all the cables & cards are good.