Roses are renowned for drooping. This tends to happen when the water hasn't been changed regularly. Air travels up the stem causing an air bubble blockage just below the head and stopping the flow of water to the flower.
You can now revive your roses. Take them out of the vase, cut the stems at an angle and lay the bottom of the stems into boiling water. Leave them for about 30seconds to a minute. Then transfer them straight into cold water. Leave them for a couple of minutes. Re-cut the stems and arrange in a vase with fresh water. The heads should now be upright and brought back to life. The combination of the hot and cold water shifts the air bubble and works as a shock treatment. Now you can enjoy your beautiful roses for longer!