this video shows disassembly
https://www.youtube.com/watch?v=XrZYYE1nvmM
and if you look you will see at 2.09 of the video when he opens it the power button is on the case and can be removed and replaced with new one
can be puchased on ebay or amazon
http://www.ebay.ca/sch/i.html?_odkw=toshiba+power+button&adpos=1t1&ul_noapp=true&geo_id=34636&MT_ID=16&crlp=83573201317_207&keyword=toshiba+power+button&rlsatarget=kwd-2894506118&device=c&crdt=0&treatment_id=7&clk_rvr_id=1044592077653&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xtoshiba+power+button+p55w.TRS0&_nkw=toshiba+power+button+p55w&_sacat=0