On how to do effective system scan for malicious software visit this link.
(e) Doing Windows Updates.
Step 1. Click 'Start' and select 'Control Panel'.
Step 2: Click on the small arrow pointing rightward at the bar (like the normal browser bar)after the 'Control Panel' and Select 'All Control Panel Items'.
Step 3: Click on 'Check for Updates' to search and click 'Updates' to install important updates if any one is available for installation.
(f) Doing System Maintenance
Step 1: Get a Screw driver handy and open the system.
Step 2: Apply a can of compressed air to remove dust from the system cooling fan.
Step 3: Unscrew the screws holding the casing and the cooling fan(if it is not held by clips).This should be done in case you can not reach for compressed air can.
Step 4: Remove all the debris carefully and put everything back in appropriate places(the fan and the screws).