Kinda confused to what exactly you did? Messy up the 'security settings'??? Thats quite a strange issue...cant view your hard drive?? how so! (more info please)
Vista Security setting stuff? <control panel> should be useful to you sir. This is where windows defender, firewall, etc is located.
Also, as always type 'msconfig' in 'start>run>' then go through and disable anything you DON'T want wanna deal with and/or startup.
Do you have 'System Restore' turned 'ON'?? If so try resorting back to a time prior to this issue(s)
Are you talking about the 'File Searching' features??;
Right click the 'Task Bar '> Properties > Start Menu > Customize > Check anything saying 'search for ...' or whatever and make sure the boxes are checked.
Again, need more info buddy. WHAT exactly did you mess up? Where? How? Huh?