Uh, capitalize capital if the word capital refers to somethign specifically(noun). I can talk about capital punishment, or I can name a stick "Capital"

Also, please watch your step, I just washed the stairway. Thank you! :D

Do you need to capitalize Capital even if it isn't at the beginning of a sentence? Hmm, the world may never know... unless you do of course. If you have an answer please call me by my home phone number.... actually try smoke signalling me because the sky is clear tonight and my phone is currently MIA... So yeah, just give me a call (or rather a signal) and contact me if you happen to know, like a good student, the answer to my perhaps extraneous and intangible mathematical problem. Thanks and good luck! :D

CAUTION:
[Proceed with utmost caution when reading this comment; readers may experience temporarily yet detrimental distraction from everyday tasks, educational initiatives, and consumption of delectable desserts]