I agree with previous posts, I'd suspect spybots or adware that are consuming resources, fragmentation, low powered processor, or your could have too many programs loading at startup. I use Ad-Aware & SpyBot Search & Destroy, they're both free & can be downloaded from
www.majorgeeks.com.
Find out if your Compaq has a Pentium4 processor (desireable) or if it has a Celeron processor (acceptable for email but not for gaming).
Nothing magical about defragging a harddrive. Bigger = takes longer, if heavily fragmented = takes much longer. Fragmented = disorganized, think of trying to find a phone number if the phone book wasn't organized.
Left click Start, All Programs, Accessories, System Tools, Disk Defragmenter. Highlight (click) the volume you want to defrag & click "analyze", it'll tell you if defragging is recommended. Anything over 5 - 7%, follow the same steps but click "Defragment" & let it run overnight 'cause it'll take hours.
You should also check to see if any clean up is necessary. Clean up = get rid of junk.
Left click Start, All Programs, Accessories, System Tools, Disk Cleanup. Choose the drive your want to clean-up, and put a checkmark next to "Temporary Internet Files" and "Temporary Files". Click "Okay" then click "Yes".
Right click the Task Bar at the bottom of the screen and left click Task Manager. Left click the "Processes" tab, then left click "mem Usage" to sort the processes by memory used ... you might be able to identify a resource hog but it's tough 'cause many of the processes (like IExplorer.exe which takes about 30MB) have to be running.
You could also left click "Performance" and look at the "Physical Memory" box which represents RAM. Your "total" amount should be some where around 768000 'cause the number is in Kbytes so pay attention to the "Available" number. If you utilize all your RAM you'll get into page swapping ( also called hard disk thrashing) & that'll definitely slow you down.
Unless you know what you're doing I'd advise against changing anything in msconfig or in the registery. It's OK to look but always leave these pages by clicking "cancel" so you don't accidently apply a change that you didn't intend to make.
Remember: A little knowledge is more dangerous than no knowledge at all.
Why?? 'cause it falsely gives you the confidence to plow ahead & most likely make the situation a whole lot worse (maybe inoperable) before a techie can straighten it out. The Geek Squad at BestBuy does a pretty good job & they stand behind their work.
Good luck