The 7490, although it is probably the decade counter I've used the most, is a royal pain in the tooshie to make work, primarily because it has four reset pins (two for reset to 0, two for reset to 9) and because it's split into a divide-by-2 and a divide-by-5 counter and they must be connected together.
So, be sure that the Qa output is connected to the clock B input and use the clock A input as the input from your source to be counted. You MUST use this configuration if the counter is to drive a BCD-to-7 segment decoder driver. If there is no readout, you can use the clock B as your main input from your source, and connect the Qd output to the clock A input. Your final divide-by-10 output will then be on Qa. The only reason for the second method is that you'll get a perfect square wave from your decade output which may be necessary in some applications. But you can't use a decoder driver in any fashion whatsoever in this configuration, for you'll never get a proper count-up sequence.
As for the resets, these are active HIGH resets, so to count, all four pins must be tied to ground or a logical LOW. If left unconnected, they will float high and strangle the counter.
Dean