E7400 65 watt max TDP at stock settings
HD 4670 Full load 64 watts
Motherboard & Ram about another 50 to 75 watts
Hard drives 8-16 watts
DVD burners 25-35 watts
And a Fan or Two 5-10 watts
65+64+75+16+35+10=265watts
So If that sounds like your system you are good to go. If you could though look on the PSU and see how many amps it has on the 12v rail?
well, if its a GOOD QuALITY 300 psu. however, i would suggest either an antec eatherwatts 380w or a corsair 400cx. the corsair is better but it has more overhead in case u upgrade something in ur comp later
If it is a good 300W PSU manufactured by a reputed company then it will surely run the setup.
But if it is an el-cheapo unit then you should change it!
Post the Amps(rating) on +12v rail written on PSU Sticker