250w power supply??? You shouldn't even be running a computer with less than 300w of power. I guess it's been functioning for you thus far, but you should know that most p4 systems have at least a 300w psu. Many computer manufacturers do things like this though and take shortcuts on essential parts. The problem is definitely your power supply. DON'T keep tinkering with your system until you replace it!! When the psu goes it can take every one of your components with it!! Some of your hardware may already be damaged.
Something in the neighborhood of a 400w psu should be fine.
I'd say you should get a quality brand. FSP is a high quality brand and they're not expensive. Here are some links.
http://www.newegg.com/Product/Produc...82E16817104935
http://www.newegg.com/Product/Produc...82E16817104953
An antec power supply would be ok for your needs too, but I've never trusted antec for systems which require lots of power and are under constant load. Not that your system falls into this category. Still, I've seen too many problems with antec power supplies. Antec is living off their reputation from 5-6 years ago. A lot of their brands are just plain unreliable and they don't seem to last.
Is it worth fixing? Well that is a bit subjective.
IF you plan on buying a new computer anyway I'd spend the extra money now on a decent power supply. So from that standpoint it is worth fixing. Depending on what you plan on using your computer for you won't necessarily need a fancy, super expensive power supply that packs a lot of juice. But don't let a high powered, 600+ watt power supply (for example) scare you! They're actually cheaper on your electricity bill than most 350-450watt power supplies because they are more efficient and they don't have to work as hard to power your system. Just because a power supply can offer you a lot of juice does not mean it's putting out that much power all the time. They're not. Sometimes it's better to by more than to buy something that meets the minimum requirements.
Almost every motherboard today still comes with PATA ports for IDE drives. The PATA port is what you plug your CD ROM and your hard drive into on the motherboard. Most modern motherboards only come with one PATA port today, and not 2 like they used to. Yes, you can still use your old hard drive on any new system, but it's probably best to get a SATA drive if you get a new computer. If you decide to you use the hard drive from your Monster computer as a slave you can still do so, but then you MUST make sure you get a SATA compatible CD/DVD ROM. The 5.25 bays are usually too far apart from the internal 3.5 bays to connect both drives to the same cable, so if you get a SATA disc drive you won't need to worry about this problem. Of course you could also buy an external enclosure and put your old Monster hard drive on the external enclosure and just plug it into the USB port to access it!
There are lots of options as you can see.