本人洗機後裝了　window xp ，但沒了音效，請問是什麼原因

你要裝返個Sound card driver，o甘咪有返音效，但係要視乎你個部機係咪 all in one 底板定係另外加入去底板裡頭，相應地搵返適當既driver咪得囉
另外usb喇叭應該係你對喇叭係usb取電，正常sound card位係有個出Audio既插孔架。

I can only type simplified chinese with my computer but I worry that it'll be messed up here, so I will answer in English.

For 音效, it is because you didn't install the sound card for the CPU. I believe the installation drive comes with the computer purchase. If the computer only has the USB port, then you can install an external USB sound card, which can be found in most computer stores.