Hey guys new to forums and need some help

. I just bought a celestron nexstar 4se I have got it aligned ok and working the only problem I'm finding is when I look at planets i.e. Venus and Mars it just looks like a circular star i have it in focus but am just not getting any detail is it something to do with the eyepiece or is the wrong conditions. Any help would be greatly appreciated on the same note I have the standard 25mm plossi and also 15mm kellner and 6mm plossi. Are these eyepieces ok to use for detail?
Thanks again
Scott