Apps Not Starting Properly - Sys. Recovery Doesn't Work

I have no idea what my sister and her friends were doing on the comp for a couple of days that i decided not to use it, but now:a few programs take forever to load or don't load at all, but they do show up under the processes tab in the task manager - after pressing Ctrl Alt Del, the task manager icon appears in the system tray, but the thing only shows up a minute later - my system recovery is "not able to protect my computer," and restarting does nothing - actually, when restarting or shutting down Windows, it stops at where it only shows my desktop background and cursor [which is still able to move] and nothing else after that, so i have to hold the power button and force it to shut off - when I right click the desktop and click on "Properties..." [or something similar to this action] it doesn't show up at all, and whenever I try to open any application after that, they don't even load at all either