Hi, want to buy a new pc and my budget is 15 to 20 thousand. its for a home usage like internet, Microsoft word work and for watching movie. please suggest a good one.

HI, you may get a very good pc in such price range..

Like:

Intel Pentium G645
Gigabyte B75/H61 Motherboard
4 Gb Ram @ 1066 Mhz
NZXT Source 210
Total 12000
Monitor 6000

Also, if you prefer AMD then I can suggest AMD config also..

As per your budget you can easily met your requirement but before giving you suggestion you are looking for an assemble one or want to buy from a single company.

Going by assumption that you need a assembled PC. Then you should consider AMD setup as well to the Intel setup recommended by Savera.
You could go for AMD Athlon II X2 270 processor and Biostar TA970 AM3+ motherboard along with what Savera has suggested.

I too would suggest an Intel config for assembling 20k computer.
Intel G645 would cost 3.5k,
biostar hifi h61s3 mobo would cost 4k,
kingston 4gb ddr2 valueRAM costs 2.4k,
WD Caviar Green 1TB HDD 4k,
local cabinet 1k,
seasonic ss400 psu 2.5k,
viewsonic 18.5 inch lcd 5k
keyboard + mouse rs. 500
a total of 23k approx
and a good enough pc would be configured.