I use a free service that i am very pleased with. I get an email when the server is down and then another when it is up. Go to http://www.uptimedog.com/ Checking is done every 2 minutes Take care buddy!
Try www.pingdom.com - they even offer a free 30 day trial with SMSs included! Reasonable cost, and they have a great service.
you can try following tools. I have installed these server monitoring tools. Zenosshttp://www.zenoss.com/, What's Up, cacti and Dude. I think these network monitoring tools may be helpful for you.