First off, we are not mind readers... we need to know what your computer is capable of and for that we need to know your specifications.
To find these out, go to Start->Run and type in dxdiag then hit enter. The info we want is Operating System, Processor, Memory on the system tab of dxdiag, now go to the Display tab and copy down the name of your graphics card.
Second test, Both of your roms Banjo-Tooie and Donkey Kong 64 may be damaged, I suggest you download a tool called GoodN64 from:
http://www.zophar.net/utilities/goodutil.html - you may wish to grab Goodwindows along with it if you are not used to command prompts.
Instructions: Place goodn64 in c:\goodn64\ and also place your roms there, go to Start-Run again and this time type in cmd. in the Command promt type CD \ and hit enter then type cd goodn64. Finally type goodn64 rename and if all goes well it will rename them to show whether they are good or not. Tell us the new filenames.
If I were to guess i'd definately say that your Banjo-Tooie rom is damaged, as for Donkey Kong, it runs fine for me (except I play Banjo-tooie on 1964 0.8.5, see Banjo-tooie faq in general n64 forum for more info on that)