Ha ha, you wont have to buy another computer!(lets hope not)
The chkdsk is that 'Scan Disc"? That you are trying to run or is it the actual defrag?
If you are wanting to defrag and thats not working then usally you can go to 'Scan Disc' and it find any errors you have on you HD, then 'usally' defrag will work, and what i mean by 'usally' is if you dont have a heap of errors and crap like that stopping it.
Also if no programs arent cause'n interferance then it will run..(both the defrag and scan disc)
Not sure if thats what you mean?