You must be doing something wrong then. Do you have a PS2 Classic with an adapter or a PS2 Slim? What revision? What method? Are you using complete dumps? Are they clean or patched? OpenPS2Loader or HDLoader? There's a whole procedure, you see.

Loading from USB has a very small compatibility list, lags during fmv due to the painfuly slow speed of the USB slot (1.1 revision of USB) and loads forever, it should only be regarded a last resort or a homebrew-loading method. Describe your issue and answer my questions and I may help you out - buying an external drive for this purpose is equal to throwing your money away when there are better, cheaper alternatives.