Even though it's been working before, the situation you are describing could quite likely be related to a jumper setting problem (I'll explain that in a second). Often when there is a booting problem with Pavillions, they refer to the repair partition, which restores the operating system, but mucks up the boot order. HP usually sets their IDE devices (i.e. CDROM, Harddrive) to "Cable Select" or "CS". To fix this you need to set your harddrive jumper to master, and your cdrom to slave.
But that is for later on... and if its only a year old, it will probably void your warrenty.
Firstly lets try and replace the drivers for your cdrom. This will identify whether the OS is running inappropiate drivers for your device, or whether your OS has detected it at all.
Click -> Start
Click -> Run
Type "devmgmt.msc", then hit "OK"
The list of stuff here are the devices on your computer.
There should be a catagory called "DVD/CDROM drives"
If this catagory is not there, then we need to check that your BIOS is detected your CDROM at all. (READ FURTHUR ON)
If the catagory is there, then open it up. Assuming you only have one CD drive in your computer, there will be a single name.
Right-click on this name, and select "Uninstall".
This will remove the drive.
The next step is to get windows to reinstall the drive. To do this, from the top menu select "Action -> Scan for hardware changes".
Windows will do a scan to find your device.
If it finds a device like your cdrom, check whether its visible in "My Computer".
If your CDROM is in "my computer", then its beer o'clock.
If there is no device in "My computer", then its likely to be a driver related issue, and since you have internet, will be fairly easy to fix. (We'll deal with that if it comes up)
The other likely situation was that the BIOS may not be detecting it.
HP have decided to be rather flippant with their BIOS entry keys, so we'll guess them after you tried replacing the CDROM's drivers.
Let us know how you go with that.
Best of luck
Regards
Angus