Raspberry Pi
Raspberry Pi
Raspberry Pi won't boot?
For me it was an incompatible SD card (Panasonic 8GB Class 6 SDHC model RP-SDV08G) but here are some other troubleshooting steps you can take:
1) Try different power adapters. You need to provide 5V at a minimum of 700mA. USB power adapters designed for iPads can supply over 2 amps so should provide better stability if you are planning to draw maximum current from the onboard USB ports. Decoding H264 video is power intensive for the CPU and GPU so factor this in too.
2) Try different SD cards, a list of compatible cards can be found here: http://www.raspberry-pi.co.uk/2011/12/16/compatible-sd-cards/
3) Try composite video out in case there is an incompatibility with your HDMI cable.
4) Try booting without keyboard / mouse in case they are drawing too much power.
5) Double-check your SD card image by inserting it into a laptop/PC and checking you can read the filesystem
6) Check the SD partitions using fdisk -l (8GB card example):
fdisk -l
Disk /dev/sdb: 8057 MB, 8057257984 bytes
4 heads, 32 sectors/track, 122944 cylinders
Units = cylinders of 128 * 512 = 65536 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000ee283

Device Boot      Start         End      Blocks   Id  System
/dev/sdb1              17        1216       76800    c  W95 FAT32 (LBA)
/dev/sdb2            1233       26672     1628160   83  Linux
/dev/sdb3           26689       29744      195584   82  Linux swap / Solaris
7) Check the troubleshooting forum on the official website: http://www.raspberrypi.org/phpBB3/viewforum.php?f=28