the OP mentioned - it is an OLD computer running on a P3 500MHz, as with most modern software the OLD computer will struggle:
1. to run on 500MHz (as most modern CPU is running at 3GHZ),
2. the size of the hard disk (probably small : heaving at the seams) to store data (as most modern computer has 500G),
3. the size of the RAM (small) will be slow for memeory access (as most modern computer will have 4 GB)
it is good to save money, but in this case the best solution is to get a new computer.
the costs to repair the OLD computer with parts and labour is pretty close to a new computer.
the benefits are clear.
with a new computer; all the modern softwares are usable, the speed will be faster and the hard disk can store more data than previously, and the speed from a new computer is faster than a P3 500MHz computer.
the hassles of more problems going out from the OLD computer: hard disk size, RAM, CPU speed are bound to come up from time to time.
and finally, if the OP do decide to repair the OLD computer, how long can the OLD computer lasts?
as there are more and more modern softwares on the markets, will the OLD computer still become compatible?
the OP may replace the hard disk, but the OLD computer CPU and its motherboard is not recognising the new hard disk.
the OP may change the BIOS setting and if it does work.....in the short term the OLD computer may pod along...but for how long?
technology has moved on.
as for the OS, the OLD computer being a P3, can run on windows 98 (11years ago) but only just because it is the maximum level a P3 can run up to.
as for any OS newer(Vista, window7), the P3 will struggle to start
just get a new computer and forget about all the problems...it is just not worth wasting time and money fixing a OLD computer.
i hope this has help.