try pulling the plug out for about 30 sec. then plug it back in and boot up.
try listening the tower when you boot, if you hear the floppy reading in a strange way repeat.
i have not found out why it does this, but i have 4 computers doing the same thing.
Dell had a bad batch of GX270 boards/power supplies. I have replaced 12 in the last 3 months and I also got them to pre-ship me 52 more, so we can replace them before they go bad. Yes it is usually the caps that blow. If you replace one without the other(P.S. MoBo), you will usually have the same problem again. When you work for the State Gov., you can't just sit and wait for them to fail. All of ours so far, have a Service Tag ending in a *****31 or *****41. And most have an "X" in it also. Just curious what ur service tag is.