RPi Lights but no boot
Ok you have a fresh RPi and you have plugged in and as a noob your super cautious that’s understandable.
You have all your lights on your RPi and you have your HDMI plugged in then you realise your TV (Monitor) has gone to standby (not uncommon) so you switch on your TV to HDMI nothing blank screen.
OK here’s what’s probably happened the RPi at start-up has checked the HDMI for a feedback signal and when it does not sense one it’s activated the composite as the default monitor the composite has nofeedback it's pure output and as the RPi does not do both (at this time) it defaults to composite.
What to do.
Well your understandably cautious because your precious RaspberryPi is fresh out of its box and your worried you will royally screw it.
Composite AV Method
If you have a composite input on your tv (it will probably be a yellow phono socket and you have found a suitable phono lead (one long enough) you can get it kicked off that way quite quickly plug in the phono both ends (TV and RPi) switch your tv input to AV and if you have Menu screen then you are in raspi-config and proably need to look at that bit of the noob guide.
One of the other options if you have a conversion plug to adapt s-video to phono or a SCART plug with phono input.
AV S-Video and Scart all support Composite input.
What to do if you don't have a Phono lead or a TV with the suitable AV, SCART or S-Video option.
Well you could look at the ssh Blind Login option that’s another safe route. This assumes you started your RPi with a network cable connected to your router. and you have a PC running Windows or a Linux desktop of some description. The fun bit will be figuring out your IP address (If your router is Netgear or a re-badged Netgear then there is a good chance your IP will be something like 192.168.0.x D-Link consider 192.168.1.x in both cases consider the x to be a low single digit number greater than 1 (guide not gospel)
You for some reason can't use either of the two previous approaches.
pull the plug Method
It is worth noting the memory on an SD card is reasonably stable as long as it is not in the process of being written too. If you have a camera with an SD card your unlikely to remove it while saving a picture but if the camera were dropped mid save and the battery compartment were to pop open you may loose the last picture but those allready on the card would more than likely be safe.
So get your TV off of standby make sure your HDMI cable is connected kill the power to the RPi probably best at the supply end of the power cable. This would be seen as a good habit becuse if the your RPi power socket wears out its problematical a second hand phone charger is by comparison cheap and easy. Then restart (yes switch off and switch on again).
If you do screw the image on your SD card this early in the game you probably don’t have much in the way of changes written to the card. Probably nothing. If your SD card is that flaky then it was probably not going to play for log any ways.
So power down and power up and if it does not work then think about re-imaging the SD card.
I have my RPi in a Lego constructed box (I had the Lego any ways). On one occasion I tried three times to get it to boot when I went to remove the SD card to re-image I found it was not inserted correctly (one edge was not in the slot.
Give your self a chance while you have few changes experiment with wiping the image and re-starting wheezy does not take too lonk to re-image you will gain confidence and it is also worth exploring the blind login option if nothing else it will teach you a little about command line.
When it comes to hardware the RPi seems to be fairly robust avoid static electricity zaps allways a no no for ic stuff but otherwise as log as your careful you should be ok.
In comparison to my first encounter with bare curcuit ic chips upgrading my 16k Spectrum to 48k would be the equivilent of toying with 400 quids worth of gear the Spectrum and the chips came to a weeks wages in real terms.