My Windows 98 computer used to work very well, but all of a sudden it started booting up only in safe mode . When I try to start it up in normal mode, it shuts down. I know that this isn't much information to deal with, but that is all that happened. The only thing that I think could have triggered this was the installation of Turbotax the day before.

Thanks for the help,
Peter

Seems that you have answered your own question.

The good:
if u have a recent full OS backup from before installing Turbotax, restore from it.
The bad:
if u don't have a recent full backup, must reinstall OS into same directory.
The ugly:
if u don't have a Win98 [FE = First Edition or SE = Second Edition] setup CD, u must either borrow or buy 1 in order to reinstall OS.

FYI in case u don't know...
The Good, The Bad + The Ugly:
http://www.imdb.com/title/tt0060196/
http://www.amazon.com/gp/product/6304698798/
http://www.amazon.com/gp/product/B0001GF2DS/

Hope this helps.

TurboTax is known for its intrusive copy-protection system that may corrupt parts of your hard drive... my advice is to avoid it completely.

A full wipe and re-format may be required in order to rid the system of its remnants.

There are several avenues to explore. This is not an exhaustive list of troubleshooting measures but should help you.

1-You may want to uninstall the "possibly" troublesome application, in this case, TurboTax.
01-Boot Windows in Safe Mode.
02-Uninstall TurboTax.
03-Reboot.

2-Restore a previous Windows REGISTRY.
01-Go in the Windows Boot Menu by hitting the F8 Key.
02-Choose: Command Prompt Only.
03-Type the following: CD WINDOWS\SYSBCKUP
04-Hit Enter Key.
05-Type the following: MD OLDCAB
06-Hit Enter Key.
07-Type the following: COPY *.CAB OLDCAB
08-Hit Enter Key.
09-Type the following: SCANREG/RESTORE
10-Hit Enter Key.
11-Choose a registry file dated before you started having problems.
12-Choose restore, the program will restore the registry file and reboot. Hopefully, if the problem relates to registry entries, it will correct the situation. TurboTax will probably not fonction correctly after restoring a previous registry file.


3-You could also use the BOOTLOG feature of Windows.
01-Go in the Windows Boot Menu by hitting the F8 Key.
02-Choose BOOTLOG.
03-As you stated in your post, the computer will reboot.
04-Go in the Windows Boot Menu by hitting the F8 Key.
05-Choose: Command Prompt Only.
06-When at the C:\ prompt, type the following: EDIT BOOTLOG.TXT
07-Examine the entries or do a search for the word : FAIL
08-This MAY give you a clue what driver/application is giving you trouble.


Countach.

This symptom can occur if the processor is overheating. In that case, it would be the motherboard shutting down, because of thermal protection on your motherboard. It's possible that PC with flaky hardware will be fine in safe mode.

Thanks for all of the responses. I will look into the TurboTax option. As for overheating, it has okay air-flow, and that shouldn't be a problem.

But your heatsink may not be seated properly! A common mistake is to put the heatsink on backwards
(especially with socket A) and not using heatsink compound. (thermal paste)