I wouldn't worry about the cpu. Unless you're up to freaky overclocking, they almost never fail. Neither does memory, however, you may have a memory type that is setup incorrectly or incompatible. For example, on some asus motherboards with the nforce chipset, corsiar memory wont work. No boot, nothing. Also, some motherboards are a little overly aggressive with their timings. They pick 2 instead of 2.5 or 3. You could also try jumpering a lower bus speed, say 100mHz.
If you know your system specks, feel free to post them. Particuarly the mobo chipset, ie intel, via, nvidia, sis.