If you can run Apple Hardware Test in EXTENDED MODE at least 2-3 times in succession. If it reports any errors then you know you have a hardware issue and need to take it in for repair. It's highly unusual it would fail after a year however if it's something like a HD they can fail at any time. Remember Apple (nor Dell or HP) make HD's they supplied by 3rd party manufacturers. In the future it's always smart to buy AppleCare, however that's water under the bridge now. If there is a hardware failure it's going to have to be fixed at your expense.
Before doing the AHT I'd also recommend starting in Safe Mode . Give that a try first. Also try rebooting in the Recovery Partion, and run Disk Utility - Repair Permissions and Repair Disk.