Bob stayed at home last sunday and did everything except----

这个except 相当于but,这是少数的可以跟不定式的词.但是因为前面有实意动词did/do/to do 介词后面的不定式符号to 省略.如He did nothing but sleep./He had nothing to do but wait./ He had no choice but to sleep.
再问： 那什么时候区分EXCEPT是介词 什么时候是相当于BUT
再答： 大部分情况下except 和but 可以替换，如all the class went there except/but Tom. there was nothing in the room except /but a chair. 但是except 后面可以跟that 从句，but 不可以，如I know nothing about him except that he is from America.