E machine wont start
Here's something you can try: If you can borrow a computer power supply rated at 350 Watts or more from someone, do the following: Unplug your power supply from the motherboard. If it's an older model (pre-Pentium 4), there will be one wide (20-pin) white plastic connector. Along one of the long sides of the connector, there's a retaining latch. Squeeze it, and gently rock the connector from side to side along its length, while pulling up. The connector should come free. If it's a newer PC, there will be a second connector with 4 pins, and yellow and black wires. If so, squeeze its latch and just pull up on it. Next, disconnect the white power connectors from the optical drives, hard drive, and floppy drive. If the internal fan you talk about is a case fan, unplug it, too. At this point, you should be able to take all of the power cables and hold them out of the case.
Now, plug the power cables from the power supply you borrowed into all of the sockets you just vacated. The motherboard connection(s) have a little nub on one side; this lines up with the latch on the plug(s). The hard drive and optical drive connectors only fit one way. The floppy connection is wider on one long edge; this sits on a little shelf when the connector is plugged in. Plug in the case fan. Make sure the borrowed unit is not resting inside the case. Finally, plug the AC power cord into the socket on the borrowed power supply. You should now be ready to push the PC's power button. Do so.
If the PC boots fine, you have a bad/failing power supply installed in it. Sometimes they just don't have enough power to boot the motherboard when other accessories are also drawing power. If more accessories than those which came with the PC were added, this makes the problem worse.
If this works, you need to replace the original power supply. With your PC turned off and unplugged, remove the 4 screws holding the power supply to the back of the case. Lift the unit out. If you can keep the borrowed one, it's simple. Place it into your casr where you removed the original one (note the unit will fit two ways, but the screw holes only line up with one of them), line up the screw holes, and install/tighten the screws. Plug in the AC cord, and boot the PC up. If everything is okay, turn it off.
Since you're already inside the case, take some canned are and dust off the internals. Be especially sure to remove any dust between the processor's heat sink fins. Hold the processor fan with a finger to keep it from spinning.
Of course, if you CAN'T keep the borrowed unit, disconnect it as above, obtain a replacement, and repeat the installation/connection steps above.
Let me know if this works.